This is a guide recomended for 5vs5 games.
It may seem a little odd but for somebody with average player skills is well fitted.

if the game lasts 30-40 minutes you don't have time to do the tanky build. It's purpose is for late game.

Armor penetration, attack speed and early damage are very good, but you can choose any offensive runes you like

I go for 23-0-9 with exhaust and ignite.The low cd ultimate is a very good escaping mechanism

I chose Tiamat because is very cheap, good damage, good for pushing and easy gold.