Renekton is a damage/off tank in this build i play him with a ranged in top lane and aggressive to minions early game play aggressive to champs mid game and aggressive to champs and towers late game. my best score with him was 27/11/4 in 5v5 game.

not a lot here Armour pen marks and quintessences to help him when against tanks Armour seals to help him be a off tank and magic resist for those stupid mages that love killing him.

I use good hands in utility so he can get into the fight sooner and use Armour and a health bonus with revive in defense to help his off tank so in late game he has almost 3000 health i basically just give him better crit chance and ability power so his spells do a lot and his normal attacks do heaps. Cool down reduction is important and giving him some DPS capabilities is good as well as well as Armour pen damage and crit damage with a bit of base magic and normal damage.

I start with dorans shield because its gives you that little bit more health early game and get boots of lucidity to make him a bit faster and so he has cool down reduction. brutilizer gives him that little bit extra damage and last whisper is a must as it is great for owning all tanks. spirit visage helps with stopping those pesky mages and guardian angel ensures that you live for longer. i sell dorans shield for thornmail to stop most DPS attackers from killing me to quickly. i then get yomumus ghost blade to increase the usability of brutilizer. then i go on to sell the boots for force of nature.

i get cull the meek first for easy farming, then i get slice and dice as it assures that most champs die when running away, then of course i get ruthless predator to take a bunch of health off champs getting Dominus whenever i can. this assures most ranged die fast and CC may take a little longer.

i get ghost mainly for laning so i can help when i am needed and revive just helps with being an off tank and scaring all champs when they see me back so soon and their on low health.

Pros
Has no mana
Great farmer
Good for laning
Good with ranged
Good against most types of enemies

Cons
Rage takes a little getting used to
Will almost always be the lowest level of everyone
When a team mate feeds you die really fast
Against Yourself or your brother your probably going to die a lot

As i mentioned earlier Renekton is good if he has a Ranged with him like Miss Fortune, Caitlyn and Tristana. Though you typically wan to put him with Mages like Janna, Karthus, Lux and Vladimir.

So he is good with and against mages in this build. He has good laning capabilities and is good at kill stealing. he has off tank capabilities and is great at dealing heaps of damage and remember Light meat Dark meat its all the same...