Sooo u r looking for a good guide for Rene ? I was looking for it to. I was trying different guides and builds to discover that one, which i am using now. As u well know ( hope u do ) Renekton is using " fury " points to use his skillz. Fury is generated by auto attacks and Renekton's skills. To master Renekton you will have to learn how to properly manage fury points.
Soo shall we ?

For me there is no other way for runes. MR , Armor , Armor Pene. Everything that Renekton needs.
MR and Armor will increase your survivability , while armor pene will decrease your targets survivability. I wont recommend dodge seals couse:
1. Renekton doesn't have any skill to help out that dodge rate. Even with masteries in dodge and 9x dodge seals from tier 3 your dodge = 4-5%.
2.They r 2 expensive.

As u can see i am using 23/6/1 build. I'll explain why.

First utility tree:
- I took Improved Ghost becouse very often I have to run to the other side of map. Its helpful with ganking and chasing.

Def tree:
- MR and Armor , why ? with your runes and those bonuses it will be a nice start for u. The longer u will live the more damage u will deal - simple as that.
Offense tree:
- What can I say here. I think it is pretty obvious. Magic pene for ult ( as it still dealing magic dmg ) , Atk spd - a little faster fury generation ( lover delay between attacks ) , Improved Exhaust - for chasing or disabling one of the enemies.

Item order like u have above. Some will not recommend Trinity Force. I'll try to explain why I took it. Even with your cooldowns reduced to 30-40% your skillz still have some cd. While skillz are on cd you have to do something , right ?. With some atk spd and crit rate it could be pretty deadly , and with 150% dmg from trinity after using skill, its getting even more deadly. Why Spirit Visage ? Your Cull of The Meek recovers hp. And I decided to enhance that mechanics. Rest of item for armor pene / dmg.

Sometimes I am making Sunfire Cape instead of Last Whisper. It's when I see that my opponets doeasn't rly care about armor.

Like above. There is a way to max Ruthless Predator first but i dont really recommend it. Hp recovering is more important for me.

Ofc Ehxaust and Ghost. Some will take Flash. It's a good choice too. Rest summoners spells leave to the others :P

Completed build - stats:

Health 2720 at 18
Health Per 5 sec 20.2 at 18
Mana Per 5 Sec 0 at 18
Armor 107.9 at 18
Dodge 0 at 18
Magic Resist 106.8 at 18
Damage 331.92 at 18
Critical Chance 55 at 18
Ability Power 30 at 18
Armor Penetration 59.93 at 18
Magic Penetration 0 at 18
Movement 436.8 at 18