Welcome to my first Mobafire Build so don't be too hard on we will ya :). Now.. i have been playing Renekton for 2 days (cause unfortunately we on the EU get these patches a day later) and i have been testing different items,skill orders and masteries and these are what i have found best for my play style. Feel free to comment and ask anything about my build.

Pros:

-Uses no mana
-Can choose to be more tanky if the team needs
-Has a nice Stun + DMG with Ruthless Predator
-Slice And Dice can be used for both chasing or escaping an enemy
-Ultimate gives some nice plus to Renektons survivability and DMG.

Cons

-Squishy early game (going to give a few tips to that)
-Uses Fury so you may need to get used to that first

I like to take Exhaust and Ghost, I take Exhaust cause with improved Exhaust you can even get enemies armor and MR Down + With ulti you can win almost any 1v1. Ghost is a good for chasing and escaping since Slice And Dice has a pretty long CD so you wont have it all the time. Other good options are Cleanse cause it gives you even more survivability, and Ignite With that you can maybe get off some kills you wouldn't get without it.

So why do i take Ruby Crystal instead of Longsword. As i said before Renekton is very squishy early so Ruby Crystal gives you some nice Health.These are your core items After that you will just take defensive items depending on what champions the enemy team has if they have mostly AP takeHexdrinker If They have mostly AD TakeThornmail If they have pretty equal amount of AP and AD TakeGuardian Angel After that go for anInfinity Edge.

(Innate): Renekton gains 5 Fury per autoattack. Having sufficient fury empowers Renekton abilities with bonus effects, but this drains Fury. When out of combat for 12 seconds, Renekton loses 5 Fury per 2 second.

When Renekton is below 50% life he generates 50% more fury. this gives massively more DMG to your skills when below 50% HP.
(Active): Renekton swings his blade dealing physical damage to nearby enemies and healing for 10% of the damage dealt up to a hard cap. Each target hit grants 5 Fury, up to 25. Heal amount is tripled against champions.

When Renekton has more than 50 Fury he deals 50% additional damage and heals for 15% of the damage dealt, the healing hard cap is tripled. Consumes 50 Fury. A nice DMG harassing and a healing ability if you really need hp wait until you got 50 fury and make sure you are in range of 5 minions.
(Active): Renekton next attack will swing twice dealing physical damage and stunning his target for a 0.75 seconds. Each hit applies on-hit effects.

When Renekton has more than 50 Fury, his next attack will swing three times dealing physical damage and stunning his target for 1.5 seconds. Consumes 50 Fury. Has a high DMG + it stuns So its a great harassing ability.
Slice: Renekton dashes forward, dealing physical damage to targets along the way. If he hits a target he gains the ability to use Dice.

Dice: Renekton dashes, dealing physical damage along the way. When Renekton has more than 50 Fury during Dice, he deals 50% additional damage and shreds the armor of targets he hits. Consumes 50 Fury. Good for Chasing and escaping but its DMG isn't very high so there is no need to max it out first or even second.
(Active): Renekton empowers himself with dark energies, gaining increased size and health for 15 seconds. While empowered, he deals magic damage to nearby enemies and generates 5 Fury per second. Its pretty much the same as nasus ultimate, got a nice DMG Per second and a HP boost + you regenerate Fury when its on.

Now Renekton is very squishy early so here are some tips for that.
First when you go to your lane you should not get into fights, at least not before you get all your 3 skills. stay behind your minions if you are laning against a ranged champion and wait for enemy minions to come to your turret if there is no ranged enemy champ in your lane feel free to go last hit few minions. it would be good if you could get a ranged champion to lane with you so then you could go hit enemy minions pretty freely and get some money. now when you reach lvl 3 you can start harassing the enemy jump in with Slice then stun the enemy and do Call The Meek and Use Dice to go back. if you really need health wait until you have 50 fury and then make sure you are in range of 5 minions and do Call The Meek.

Thank you for taking a look at my build/guide Please feel free to say that i should add something to my build, And remember Kill steals are good for your team (more money) :)

P.S GL and HF with playing LoL everybody.