Not Updated For Current Season
Greater Mark of Desolation are there to support your damage throughout the entire game. Since Renekton is an entirely physical damage hero, we want to ensure the damage output is there the entire game.
Greater Seal of Evasion is a must for any high health, physical damage hero that has a close-range attacks and abilities. Renekton fills all of these categories, so grab them.
Greater Glyph of Scaling Cooldown Reduction are for Renekton's abilities, since he is a character without mana, he is a hero that needs cool down reduction. Now since he doesn't have an ability that you can use harass your opponents early game, I suggest getting per level over flat.
Greater Quintessence of Health because they are just awesome, a free 100 health at the beginning of the game is absolutely priceless and since you are going to want to farm creeps with Cull the Meek, you will need this.
In offense, we have poured in 21 points for the simple fact that Renekton has a lot of AoE and high damaging abilities. We are going to focus around doing damage for the most part of this build, as it will only help your farming. Now why did I put stats into the ability power side of Renekton? Because he still has that one spell that can use the extra percentile and deal a higher rate of damage.
As for the remaining 9 points, they were put into defensive to maximize the Greater Seal of Evasion that we have, putting his dodge up to around 10% of the time. However, I didn't spend the extra points to get it all the way up or include the speed because we really want him to tank as much as possible, rather than chasing down heroes. Your main role is to soak up damage while dealing it, not running around during battle.
Renekton is a close ranged, melee hero. All of his spells require him to be near a target to deal damage. Luckily, he has a pseudo flash to get him around the fields of battle.
Firstly, we have Cull the Meek. This skill is where half of your damage and survivability come in, each swing has a large AoE that only gets bigger and it heals you when it damages enemies.
Next is Ruthless Predator, the only form of CC that Renekton has. It will stun a target and attack it multiple times. This skill can offer great damage throughout the game, but I prefer to save it for late game because you want more AoE than single target.
Third, we have Slice and Dice offers Ren the other half of his damage and survivability. It has tremendous damage in the middle of battles in combination with Cull the Meek and as a plus, can be used to escape over walls and traverse terrain quickly.
Dominus is the closer for Renekton, an ultimate very similar to that of Nasus. I suggest that you activate it when in range of two heroes to get it's full effect. Always save it for battles where your opponents are high health and won't be easily taken down, as this ultimate will surely turn a battle into your favor over time with the large survivability upgrade and a buff to all of your existing AoE.
For Renekton, the common must gets are Ghost and Exhaust. Ghost allows you to quickly maneuver in and out of battle, while Exhaust ensures that you shut down high powered DPS. Either can be used Defensively or Offensively, so their choice is obvious here.
I suggest no other summoner spells, as you don't need more damage, nor do you need additional survivability. Anything that the other Summoner Spells offer, you can get in-game.
Starting off, grab a Long Sword and a Health Potion. I prefer bottom lane on either side, but go top if you can get the solo. You really want to farm rather than harass, so keep that in mind. On your first trip back, you want to buy Ionian Boots of Lucidity. Return back to your lane and continue to farm, tower hug if need be. You should only go for hero kills if it is nearby your tower or you have no chance of dying. Renekton can only Slice and Dice into a turret, Cull the Meek once and Slice and Dice back out, but will still suffer an attack on a turret unless you get good at performing this quick damage.
As the game progresses on, your next item is a Spirit Visage and you want to start building your Frozen Mallet now. Alternatively, you can get The Brutalizer first, but skip Youmuu's Ghostblade and get the Frozen Mallet right after. It makes you a great tank and chaser, two things Ren is exceptionally good at. Following this, get a Sunfire Cape to maximize your survivability and how much damage you deal by simply existing. Finally, you can choose to make a Youmuu's Ghostblade or a Guardian Angel first, it is up to you. I chose a Guardian Angel because it offers both Armor and Magic Resist, but if their team is heavily stacked in either category, you can choose to grab Thornmail or Force of Nature. I choose to not go with Banshee's Veil because the Force of Nature offers more with all that health you have stacked up.
Just remember that Renekton's true strength lies in his ability to deal damage in an AoE and should not be built towards his auto-attacks. I suggest this build over others for the single reason that you can maximize how much damage you deal in large battles and those against multiple heroes. This build utilizes the cool down reduction built into the game as much as possible, making you the greatest tank possible: You can absorb damage, deal it back out in a large area and aid your carry in just softening down your enemies.
This is not only the most damaging build with Renekton that I have seen/used, but you are so hard to kill even when you get focused, that it doesn't matter. Just pop Dominus in a teamfight, then spam Cull the Meek, Slice and Dice with a Ruthless Predator on a DPS when it comes off cool down.
I hope you enjoy Renekton, the Butcher of the Sands (even though he is a crocodile).