He's probably not gonna be building GP10s. Just build some CDR with Kindlegem---->Locket, get a Sightstone, and harass.
You're also playing a champ that usually has a very scary lategame when fed in the position of support, so he's not gonna have a lot to contribute to teamfights. Mundo's best when he can carry. --- "Whats the penalty for dodging in ranked?" "Phreak comes to your house and punches your screen."