I have this Renekton build to be the best i have tried many and this one allows for good health end game, very high armor even early game and over 100 magic resist after wits end. You will generally always want to go top everyyy time you can harass so incredibly well by lvl 3 and depending who you are going against even level 1. You can escape ganks from junglers pretty easy due to flash and if you get double e.

PROS
Very tanky all game
Good harass all game
Amazing ult that turns the tide of fighting
A stun and an escape
A healing Q which works very well to also clear minion waves
Croc man

Cons
His rage can be annoying mainly early game.
He can sometimes get out laned by a very good Caitilyn or far ranged
I find people actually do focus me a lot
Not someone you want to build full tank but not someone you want to build close to full damage for it wont work.

I have found these runes to be quite good honestly and yes you can choose between all arp or ad for reds i generally do a mix between but for quints i keep it to the health per lvl ones personally helps a lot late game with nearly 150 extra hp

I do enjoy the defense masteries the most because they allow for an all game tankyness that you just dont get from going full into offense or points in utility. You could in fact go into offense if you like for a few things like the extra damage and maybe the bit of extra life steal but 3% isnt much. I do like the last mastery in offense but compared to the all game tank you get from defense i found defense over weighs the offense.

For items you can choose between either dorans blade or shield i generally take the shield first than my first b ill get boots and the blade. After that i do rush sunfire cape while also getting wards for myself very needed for top. After sunfire youre generally tanky enough for most of the game and it does allow you with just this one item to play a lot more agressive. Black cleaver with the passive and damage makes it amazing. After bloodthirster is probably one of the biggest damage pumps youll notice while playing. Your W with 50+ rage will generally do at least 1/4 of someones hp depending on who it is. ive had it deal over half to carries and during the stun deal even more. The wits end for MR and the on hit is very great combined with W. And than atmas for the extra bulk and you get to hit hard and even crit more.

I like to max my W first because i feel its (other than his ult of course) His most important ability on him. And putting the 2 points in his Q at the start for a bit more harassment and healing from it. taking E at 3 or before in some cases is A MUST it allows you to dominate the lane at the point with just one simple move. E in W next Q than E out and they can never do a thing about it.

I like Exhaust and Flash the most but i have found that if you do get the solo top lane sometimes taking Teleport and Ghost also work really well on him. Not much to say about summoner spells with last patch honestly can take anything other than clarity and smite and be fine.

I have played Renekton for quite some time and i enjoy him a lot and i feel with this build i have it depletes any of his negatives that he has. And allows for a very bulk tank like champion who can deal out enough damage to compete with none tanks. And I can nearly always take anyone on 1v1 sometimes even 1v3 ive done at a turret with a good timed ult. Hope you enjoy and try out before down voting or up voting please :)