I have created this Renekton guide because I find it most useful in any situation by playing Renekton. This build will let you stay substantive with Renekton, in almost every game, against almost every opponent.
Already in the beginning of match when you own a Doran's Blade and you got your full Rune Page setup, you will definitely dominate your lane(Solo Top)

Early game
1. Start with a Doran's Blade and go right up to the Top Lane alone. Take Cull the Meek at Level 1
2. Now start to farm, but be careful at the same time, because you are not that strong without your Combo. Remember to use Cull the Meek to lifesteal from minions or your opponent.
3. When you have your combo ready, which means you have all your 3 abilitys ready: Cull the Meek, Ruthless Predator, Slice and Dice
The combo is being performed by managing all of your 3 abilitys in very few seconds. Here is how you perform it.
Combo: Start by using Ruthless Predator and then use Slice and Dice to get in close range to your oppenent. Now you simply attack your enemy champion and because of Ruthless Predator, the enemy will be stunned. Afterwards you have a short time to deal damage with your Cull the Meek and your basic attacks. Additionally you now have the opportunity to use Slice and Dice again and choose to flee or continue harrashing your opponent. By using this combo early game, you will definitely have a big chance to completely dominate your lane.
4. Buying the items The Brutalizer and Ionian Boots of Lucidity in early game will keep your damage output high as possible and your cooldowns low as possible. The only issue about this build in early game, is that you are not that tanky yet, therefore you need to care alot and notice all SS and upcoming ganks in your lane.

Mid game
1. As soon as possible get a Phage, it will give you more health to stay longer in fights and your basic attacks will also slow your enemys. With Phage and Ruthless Predator you will have alot of dominating CC that can help you reach kills and avoid enemys to flee or kill your teammates.
2. Now go right for Frozen Mallet by building it on your Phage. Frozen Mallet will also make your basic attacks slow your enemys movement speed and it will give you alot of health. Therefore you can now begin to play a bit more tanky, not just in your lane, but also for your whole team. That means, it's best if you take as much damage in teamfights as possible, so your teammates can deal alot of damage to your opponents.
3. Get a Chain Vest as quickly as possible and build up Atma's Impaler on it. The cool thing about Atma's Impaler is that it converts 2% of your max health into Attack Damage, this means that you now will deal alot of damage because of your Frozen Mallet. Additionally Atma's Impaler also gives you Armor so that you can stay more tanky against Attack Damage and it will also give you Critical Strike Chance. Renekton don't really need Critical Strike Chance so much, but it's always good to have though.
4. Keep on being the tanky one for your whole team's enjoyment, but still remember to farm and care for ganks, even though you have a great setup of abilitys and Summoner Spells to escape.

Late game
1. This is here your really tanky item comes in, actually the Warmog's Armor. This item will give you a huge amount of health and because of your Atma's Impaler it will also give you tons of Attack Damage. Warmog's Armor can stack up health equal to your farm after you get Warmog's Armor, this means that farming alot after you get Warmog's Armor is a very good idea. But you still need to remember your roll as a tank in your team, so don't leave your team in situations where a big teamfight could occur.
2. Normally you won't reach this section, because a match doesn't last this long. This section will often occur in between 30-40 minuttes in the game, by this time people will very soon have gotten their full build. Therefore you have to care alot and play very strategic and go together with your whole team, so you can gank your opponents or be ready for teamfights. A very importen part in late game is Baron Nashor, it will give you a very importen buff that generate faster Health and Mana, increases your Attack Damage and Ability Power. Therefore it is importen for the whole game allways have Baron warded, so you are ready to steal the Baron Buff from your enemies or to make sure Baron is free to kill. But again, remember to play the tank for your team and try to engage for your team with you Ruthless Predator, so you can stun your opponent.