Renekton is a very unique champion, being one of the few which uses RAGE. At 50 rage, his abilities can be boosted quite nicely. Renekton is, in my opinion, best laned as like someone similar to fighters like xin zhao.

This guide is for a tanky-dps renekton, which can be played well around mid-late game.

This is also my 1st guide :P

Pros:
-Powerful early game
-Powerful stunning attack
-Tanky with ult
-Strong later in the game
Cons:
-Unlike nasus, renekton gets easily raped when in a huge gang fight if aimed
-Cost alot to buy

As you would be playing a tanky DPS build, it would be better to take Red armor pens, yellow armor and blue MR runes.

Alternatively, you can also get atk speed Blues.

Armor penetration IS IMPORTANT FOR RENEKTON.

Doing a 21/9/0 ensures that u still have early game tank-ability and yet have some late game armor pen power :D

Alternatively, you can also get 0/21/9, if u need that extra tank.

For items, i read somewhere on this site that it would be better to get an early PHAGE and BRUTALIZER would give renekton that extra UMPH that he needs. True enuf it actually works.

By building into a Frozen mallet, u get that extra HP that would go nicely with ur atma's, pumping up ur dmg, and in addition with a warmog, ur late game dmg would be above 200.

If ur wondering y there isnt an AS item, that is because most of the time u spend in a fight would be used spaming ur Q,W and E.
Also, ur stun has a long animation, and takes up half the stun time, so not much use relying on AS items. :D

Taking stun 1st prevents you from getting raped early game by bush-people.

Thou Cull-the-meek may seem to deal pathetic damage early on,it would hit like a truck later on when u get some armor pens.

taking slice-and-dice at lvl 3 gives u the capability to irritate the enemy, by using the foloing combo: Slice in, Stun, cull and dice out.
It can also be used as a chasing tool, using the foloing combo: Slice in, stun, cull, dice forward.
using similar combos, slice and dice can be used to get out of tough situations and tight spots.

Finally, ur ult is similar to that of nasus, meaning u can use it to tank when appropriate.

IGNITE - for those who are going for the kill, i usually DONT take this as i dun like to KS other.
EXHAUST - Its a good spell, The slow and stuff is good. I usually take this spell with flash.
CLENSE - Good against a CC heavy team, but take only if ur building really tanky.
HEAL - One of the most useless spells later on.
REVIVE - I dont see any1 using this anywhere and u shouldnt either.
SURGE - this new spell is kinda awesome, but it isnt suggested, unless u feel that u nid the attack speed.
TELEPORT - U can take this spell if u think that ur opponents likes to have some1 like yi to push ur lanes, where u can tp over and pwn his skinny***.
GHOST - Can be used to replace flash or exhaust if u think that u cant deal with highspeed chases.
RALLY AND FORTIFY - No, unless u can use them well.
SMITE - UMADBRO?

Renekton is best played when harressing enemies early game and tanking later on. If u can utilize his rage meter, ur own ur way to success. Remember that armor penetration is REALLY important with renekton, and change ur build accordingly to the enemy's team set-up.