Renekton as i see him, is a melee OT bruiser.
He can sustain long in lane, farm well, take initial burst dmg in TF's and do tremendous dmg Early/mid/late-game. I hope you like and want to try this build and comment. Let me know how it worked for you, and what you think is missing, or if something is useless.
Enjoy :)

After FON you have some different options. Either GA, Randuins Omen or another WA if you think you lack the health, but remember if they got %health/dmg items or spells, (vayne's silver bolts, Madreds Bloodrazor etc. etc. buying a 2nd WA may make matters worse. Frozen mallet can be bought after a wriggles lantern (not switched!!!) if you feel like it for lifesteal, additional early armor and free ward every 3 min.
You can also buy lifesteal/dmg/att.speed if you want more dmg, but i think you should only do this if you are tanky enough to sustain quite a while in the teamfights.

The idea behind the skill setup is to gain the harrass combo of slice + call the meek + dice out at lvl 2, then add stun at lvl 3. Max cull the meek at lvl 9 for heal and dmg (minions can be farmed very effectively with cull the meek if prepared properly)+ it is essential for your combo. If you lack health, w8 for 50 fury. If you have that advantage already, you may want to use 50 fury to empower ruthless predator, for the longer stun and additional dmg.

I get defense in Seals and Glyphs, and Arm. pen in marks + quints to get early dmg with Q + autoattack. Renektons autoattack is weak in the early game with these runes, but your call the meek and ruthless predator combined with some harrasing auto-attacks should do enough :)
This will make you deal sufficient dmg, and sustain through same.

9 points in offense is enough! The lack of tankyness for more attackspeed and crit dmg is bad in my opinion, since 21 points in offense will give you a great early game, + it greatly improves your lategame, combined with the chosen items. More health (%) = more dmg gained from AI.
And the movement speed when above 70% health should get you an advantage against your opposing top, if you play correctly and stay above mentioned health.

I take flash and exhaust because then i'm able to pick a target to destroy and make him/her leave the battle or focus me. Flash is great for solo top, and late game and whatever. I like flash for this guy. He does have slice/dice, but in larger tf's it has a fair CD, and sometimes you just need the extra distance, whether youre running or chasing... + combined with slice and dice you're able to travel far, and catch almost any1 with this + exhaust!

Your main role is to farm a lot, harras when able and kill if you get the option.
Mid game you farm, push and roam mid for gank, or steal enemies red or give to jungler if ad carry got your red. Late game you focus stun their highest dmg threats, while keeping tanks and cc's of your carries. WIth this build you should be able to survive any initial burst + sustain in TF long enough to finish the opposing team.

I often play duo-qeue with my buddy who jungles. He is either maokai/trundle/udyr/(fiddle).
The combo of having 2 OT's instead of 1 major tank, is to have 2 ppl who watches over your carries, while being able to do enough dmg to your target so he/her will retreat.

Renekton is not so dependent on items as you think. Ofc if you are GREATLY underfarmed any champ will have problems being sufficient, but if your early game is lost with this guy, it's still easy to come back late-game, if you farm properly. I have sometimes given first kill top, and then taken 1-2 myself because he is able to harass so good. Suddenly you have the advantage, and when the opposing solo top wants to finish you because he/her has ult rdy + whatever summ. spells, you pop ult and gain a great amount of health and dot + you suddenly have enough fury to gain furious call the meek + ruthless predator in short time...

All in all i hope you like this build, and if you don't, feel free to explain why with constructive critisism.
-Dorcastner