Welcome! I want to show you my Renekton build some other things.

So... runes...

On mark slots set greater mark of desolation x9
On quintessence slots set greater quintessence of desolation x3

This runes are most important for Renekton because his skills except Dominus are physical skills which are dealing physical damage and buffing only from attack damage.

Other slots

On glyph slots set Greater Glyph of Scaling Magic Resist x9
On seal slots set greater seal of defense x9

This runes are for defense and magic resist

My masteries are 25/5/0
I set 25 points for Offense because i like to watch big damage :P

But for Renekton the most important masteries are Weapon Expertise , Sunder and Sorcery because his skills are dealing physical damage and his skill cooldown really slow.

I start with Doran's Blade.

I watch to harass the enemy with my skills and the most important i wait for last hits on minions. Just to farm gold easy. When you collect gold for Ionian Boots of Lucidity go back and buy them. But if you have to go back because you have low health or you are dead and don't have gold to buy Ionian Boots of Lucidity then buy Boots and one or two Health Potion. Its very important to buy this boots because of your skills.

Second good item for you is The Brutalizer which gives you armor penetration, damage and cooldown reduction

When you buy The Brutalizer buy Ruby Crystal and Long Sword and finish it to Phage.

After that when you buy Phage collect gold for Spirit Visage for more cooldown reduction and health

When you buy Spirit Visage buy Giant's Belt for more health and when you buy Giant's Belt finish Phage and Giant's Belt to Frozen Mallet

After Frozen Mallet buy Chain Vest and Cloak of Agility. After that finish this items to Atma's Impaler

When you buy Atma's Impaler buy Chain Vest again and one Giant's Belt and finish it to Sunfire Aegis

Your last item is Youmuu's Ghostblade and set it on first slot of items for easy activating

When i start game i start with Ruthless Predator for stun and high damage.

On second level i take Cull the Meek for damaging and healing

On level third i take Slice and Dice to get easy to the target and nice harassing with Slice and Dice Cull the Meek and again Slice and Dice to get out of the enemy

On high levels like forth and fifth i upgrade my skills depends on enemy champions and their damage. I mean if they deal me high damage i upgrade most Cull the Meek to heal myself or i upgrade most Ruthless Predator to stun and high damage ... on level 4 targets like Twisted Fate Ashe Teemo die very fast from your skills. With one using of Ruthless Predator on 50+ fury i take 60% of their health points.

When you reach level 6 take Dominus

And thats all for skills everything depends on your skills with Renekton and your playing style

This spells are very important but they too depends on your playing style and depends too on what role you take in the team.

If you are the tank and you want to survive (and your team dont have support) take Heal

If you are the damager its good to take Ignite and Exhaust to debuff the enemy players bur be smart. Dont use exhaust on enemy players with Quicksilver Sash