Against AP Heavy:
Merc Treads, Negatron, Rylai, FoN, Sunfire, Abyssal Sceptor.
Against AD Heavy:
Merc Treads/Dodge boots/Sorcerer, Heart of Gold, Sunfire, Rylai, Will of the Ancients, Randuins
Build tanky so you dont get bursted down, your 1 v 1 presence is quite strong after you survive the team fight and need to go on to smaller skirmishes.
Best option is to enter team fight indirectly, cutting in from the side and surprising your enemies.
This, so that you won't get AOEd or sniped down slowly. He is kind of like.... olaf i guess