what's up with the late Cho carrying in 3v3s lately. Almost unstoppable, but fun to play against. Anyways how do you build against him.

mr and health

You must target him mid-game.

Most people will ignore Cho'Gath in mid-game because he has a lot of health but little damage, so it's just easier to kill his teammates; however, if you don't kill him mid-game, he turns into a late game monster (pun fully intended). Killing him will half his stacks on his health, and he'll be weak.

I'm not saying target him first in a teamfight, but it's necessary to hunt him down occasionally when you see him alone.