Alright well, this is my first build and here goes nothing. To me, Renekton has to be one of the worst champions to figure out how to use. First off, his cooldowns initially blow. Secondly, he can be a major pain to play first few games. So here is my brief take on how to build Renekton in most games.

I take
Armor penetration Marks Greater Mark of Desolation
Health per level Seals Greater Seal of Vitality
CDR per level Glyphs Greater Glyph of Scaling Cooldown Reduction
Armor penetration Quintessences Greater Quintessence of Desolation

The armor penetration marks/quintessences, to me, are the best asset anyone can have for almost every melee based champion. Armor is a major pain. I personally hate it when I see a Rammus with two Warmog's Armor, a Randuin's Omen, a Sunfire Aegis, and a Force of Nature solo a turret with two champs on top of him. Maybe thats just me. But on a less exaggerated note, seriously, the armor penetration is key to building Renekton successfully.

I take the health per level seals for a little boost of survivability. It may not be much, but usually these seals will allow me one or two close calls within one game. So, the seals may be debatable, but I personally prefer Health per Level.

The glyphs can go two ways. I take cooldown reduction per level glyphs simply because Renekton's cooldowns can be a major pain. I do per level because I enjoy the late game assistance more than early game. Flat damage glyphs are another option.

The masteries listed above are the masteries that I take. 21/8/1.

Personally, I feel that augmenting ghost by taking a point in utility is totally worth it. These masteries have gotten me through many a game on Renekton. The only thing I would really alter would be whether or not to max Armor or Magic Resist in Defense tree, but it really doesnt matter unless you know who you are going up against, but usually i take the extra point in Armor over Magic Resist.

I use Exhaust and Ghost.

To me, these spells are the most useful.

Ghost - This spell is extremely useful to Renekton as both a getaway and a catch-up. This is invaluable to you as the game proceeds and should almost always be used. This could be exchanged for Ignite or some others though.

Exhaust - Renekton does not normally have a slowing ability. Until you get Frozen Mallet which is late game, you have no slow. I may swap out Ghost for some other abilities, but I never swap out Exhaust for anything. I always play Renekton with Exhaust. This spell makes for easy kills or a smooth getaway.

Options:

Ignite - Some players may want to swap Ghost for this spell. I can see where this is going. Ignite allows for an upper-hand in 1v1 fighting and in most group circumstances. If I were to exchange Ghost for anything it would be this. I believe though, when Ghost is lost, some survivability is lost, thus taking a risk that I am usually not willing to take.

Cleanse - I generally do not use this spell. It could be used in place of Ghost to get out of most CC and to save your life. I personally prefer Ghost, but this is almost equally as good in the survivability aspect, but has little offensive assistance, so...

Heal - Well, this isn't necessarily a bad idea, but you should be able to survive off of Cull the Meek pretty easily. I say no, but its feasible.

Flash - Ehh. I use this for other champions. To me Renekton doesn't really benefit all that much from Flash, mainly from its long cooldown and short jump when your survivability should be good enough to run away with Ghost.

Now that we have talked about the order in which to get the abilities, let's talk about their multiple uses. *Note* all spells reduce cooldown as they rank up (exception Dominus).

But first lets discuss fury. Fury is similiar to rage in that you start at 0 and have to gain it, when not in battle it goes down to 0. The difference is... that all of Renekton's abilities initially cost nothing. This is countered by long cooldowns. Make sure you have read Reign of Anger and understand it first before going on. Any ability used when over 50 fury is had, will be consumed. This means that you cannot choose whether to activate the furied version of the spell, you just do it. The exception is Slice, because only Dice takes fury. The consumption of 50 fury GREATLY enhances abilities, but takes a while to gain back, so make sure it is used wisely.

Cull the Meek - This spell is your life line. Not only does the spell do a significant amount of damage to all units around you, but it heals you for 10% of the damage dealt. This has a cap which increases each level because Riot does not you jumping into a huge wave of minions and all of a sudden gaining all your health back with one move. Therefore, this is the most important spell to Renekton and should be treated as such.

Ruthless Predator - This spell is a fairly good stun with a reasonable amount of damage attached to it. Ruthless Predator is one of those "next attack will" deals, so make sure you do not waste it on a minion. This spell makes you attack twice (three if 50 fury) and stun for a fair amount of time. Ruthless Predator is a major pain for those being hit and should be used only on champions and never on a minion. Also, note that this spell applies on hit effects. This means that if this spell is used with 50 fury and you have Black Cleaver then all 3 stacks will be applied immediately.

Slice and Dice - This is the harassment force of Renekton. I will have another section devoted to laning strategy, but essentially this is an extremely versatile move. This move does allow you to jump through walls like [Tryndamere], but does not have quite the range of Spinning Slash, so be careful when trying to jump through walls/trees. Note that Dice is only usable if Slice hits a unit, such as a minion. Therefore, you cannot dash twice in one direction unless a unit is in your path. This severely limits the capacity to use this ability as a getaway. Also note that Dice applies an armor reduction debuff if used at over 50 fury. Most people tend to overlook this and only use Dice as a getaway or small amount of damage. The application of this armor reduction is crucial to maximizing Renekton's damage output. Note that only Dice takes fury, not Slice.

Dominus - Be careful when using this move! The cooldown is a major pain in the butt. Don't waste it. Do not activate Dominus until you are absolutely sure the fight is underway. This spell does AoE damage to all those around Renekton and increases his health. Most people stop here. But make sure you understand that when Dominus is active, Renekton gains five extra fury per second. Keep this in mind when you think of timing the activation of the move correctly as not to waste its duration. Dominus can also be used as a getaway in desperation since the spell increases your health by a sizable amount. Also, if you are 1v1 with someone and they are just barely going to win, wait to pop this until the end when they think they have you, then you gain a couple hundred health and damage.

Okay...
Q - Cull the Meek
W - Ruthless Predator
E - Slice and Dice
R - Dominus

Some builds will say to max Ruthless Predator before you max Cull of the Meek. Most everyone agrees that Slice and Dice should be maxed last. Here is my argument against maxing Ruthless Predator first:

When maxing Ruthless Predator first, I found my survivability significantly decreased. This is because I did NOT have the required healing capacity supposed to be gained by my Cull the Meek ability to heal myself in times of desperation. Also, most people overlook the sheer force that Cull the Meek outputs at high levels. Cull the Meek when with 50 fury and at rank 5 does enough damage to wipe out an entire minion wave in one swipe and heal you for a large portion of your health. By maxing Cull the Meek first, Renekton can survive longer in fights and dish out some major force to all enemies around him. Ruthless Predator is extremely significant for its stun, but the damage is less important when compared to that of Cull the Meek, given the heal percentage.

Not only does maxing Cull of the Meek increase damage and healing, it lowers the hellacious cooldown with each level. Enough said, max Cull the Meek first since it is your survivability.

Here comes this discussion, possibly the most important discussion on any build's page. So, here we go with items.

Core Stats

ArP - Armor Penetration
CDR - Cooldown Reduction
Dmg - Damage

Core:

Ionian Boots of Lucidity
The Brutalizer
Phage

To me, this core cannot be altered in the game and successfully play Renekton late game.

Ionian Boots of Lucidity - The reason I choose these boots is to deal with Renekton's massive cooldowns, especially early game since they reduce as you level up. Really, he gains nothing from Berserker's Greaves and I could see Mercury's Treads. But when it comes down to it, you want these boots early game.

The Brutalizer - This item gives CDR, ArP, and Dmg... Wait that's everything we want? Sweet, no questions asked here I hope.

Phage - As the game gets going, you will find yourself in a position where you have less health than you want. I use Phage to have some survivability and increased health with a little bit of Dmg. Also, the slow on it is very useful since Renekton does not naturally have a slowing ability. But, the slow does not really kick in until it is upgraded to Frozen Mallet late game.

Mid-Game:

Okay, well Mid-Game is where Renekton usually thrives. This is your time to own the enemy and dominate the field. So I have geared these items to push for your positive stats and keep you as a survivable champion with major Dmg.

Black Cleaver - This item was almost made for Renekton. Check it out! The added Dmg is wonderful to any good melee of course. Truly, this is just enough ATS (attack speed) to push Renekton to his potential. From here, you don't need any more ATS and will be fine. But it's passive's combination with Ruthless Predator is truly amazing! When you use this ability with 50 fury, it applies all three stacks of Armor Reduction immediately! Thus, this item really cuts through all of the opponent's armor especially with your ArP runes and The Brutalizer.

Frozen Mallet - Well, this is just like Phage but better. It gives more health which is a huge plus to me and a little more Dmg is always good. But the REAL kick comes from the passive. All of Renekton's attacks now slow the opponent. Since he does not naturally have a slowing ability and Exhaust has a huge cooldown, this passive greatly increases the ability to kill opponents.

Youmuu's Ghostblade - Essentially, this is an upgraded version of The Brutalizer and with some added bonuses. The extra ArP, Dmg, CDR, and CrC (critical chance) are wonderful for Renekton. But really, the true use of this item is hidden in the active. When activated, the Ghostblade gives a nice movespeed buff and a nice ATS bonus. Once you have the ghostblade, it will be impossible for any enemies to get away. Essentially you have Exhaust, Frozen Mallet, Ghost, and Youmuu's Ghostblade to keep enemies from getting away, or to get away yourself. This should push you over the edge to a large extent to be a nightmare to deal with, with your ability to traverse the map extremely quickly.

Late Game:

Bloodthirster - I think it is widely accepted that this item is the most efficient use of a B. F. Sword. The little bit of lifesteal helps, but isn't absolutely necessary because of Cull the Meek's ability to heal you. But using this item as you would on any other champion, maximizing buffs from kills, can push you to be a wrecking ball of Dmg, even though most games do not last long enough for you to get to this point.

Guardian Angel - If the game makes it this far... WOW, but I believe the best move at this point would be to sell Dorian's Shield and buy this. It gives a huge push of survivability with the whole resurrection idea and a good amount of armor and magic resist. This should be the final item to complete the Renekton build.

Options:

Spirit Visage - This is the most useful item for Renekton not in this build. Arguably you need it early game. If you want to push early game, get this before the Ionian Boots of Lucidity, but that's pushing it gold wise, so I usually do not get it. This item does increase the health received from Cull the Meek and has nice CDR. Overall, good for Renekton, but not all that necessary.

Force of Nature - If the opponents have a large portion of AP casters. YES. This is a wonderful counter to most casters. Unfortunately, it is rather costly, so it's really only for certain scenarios with a lot of AP casters.

Mercury's Treads - This is a fairly viable option when it comes to defense. But once again, with out that CDR from Lucidity... It is really hard to be an effective member of the team with this champion. Overall, it's viable, but not too smart.

Laning is fairly straight forward with Renekton. Be in a position to get most of the last hits. Be the aggressor, this champ is made to harass and thrives from it.

Renekton is probably one of the easiest characters to solo lane on, once he is fairly understood to you, feel free to solo mid, or solo against two while a teammate jungles. This way you are ensured all minion gold and exp.

Anytime health is low, use Cull the Meek (preferably with 50 fury) to gain health. Keeping this in mind should keep you fairly sustained and easily laning without much recalling except for items. Do not be afraid to fall back and simply jump in for Culls every now and then to heal. Defense can sometimes be the best offense, especially with characters new to you

Harassment

Begin harassing at level 2 with the advent of Slice and Dice. When you have 50 fury, simply Slice through the minion wave, use Cull the Meek and Dice back out. It is really that simple. This strategy will put a major hurting on the lane opponents and be fairly oppressive. Once you have Ruthless Predator, use that before Slicing in, this will cause you to stun your first target (make sure it's a champion). Note that Ruthless Predator will take 50 fury, so it would be wise to wait till close to 100 fury before Slicing in, hitting with Ruthless Predator, slapping down a Cull the Meek, and then Dicing out.

Use bushes to your advantage before Slicing in. Take into account that you have to go through the minion wave in order to have Dice though. Try to use Slice and Dice to surprise your opponent.

This simple harassment strategy if done correctly will keep the opponents on their knees. The only challenge comes when solo laning against a champion like Tristana who are not squishy, are ranged, and are fairly powerful. This should only be done by fairly adept Renektons and should be avoided even then. Ranged champions in general are harder to handle than melees for you.

Try to get a caster as a laning partner. Tryndamere and a few other melees like Master Yi make good laning partners. Try to avoid most melees that don't hit too hard or that are fairly slow, Garen, Xin Zhao, etc.

Alright so now you have seen laning, now let's talk about Grouping up.

Ganking

Renekton is a great ganker if you slice into the enemy champion from behind, allowing you to Dice back behind the champion, making it difficult for the opponent to run away. Renekton has to have the element of surprise for ganking though, wait in the bushes and strike at the opportune moment: Patience.

Big Fights

The main flaw most Renekton's have lies in the fact that they simply activate Dominus too soon. Do not activate it until you know the fight has placed itself on one battleground. The duration is wasted if you spend it chasing the enemy team. Other than this, it is fairly simple to explain but almost impossible to master. Simply know what each ability does with fury. Use dice with fury to lower Armor, and use Ruthless Predator with The Black Cleaver with fury to reduce armor like crazy. Once Dominus is on, fury will be generated like crazy and you will dish out huge Dmg. Also, do not run away because you have less than 1/4 health, one well placed furied Cull the Meek will heal you for enough to keep going.

Turret Diving?

Most Renektons end up being greedy. Do not turret dive unless you are willing to use Dominus to get out. You will die. :)

So thanks guys. I hope I helped. This is my first build that I have posted, leave a comment and vote up! Thanks guys, I hopefully will keep updating it as I learn more myself.

Peace!
Janca