Mundo is a top tier DPS, but he's a tank first. As for top tier in the game, I can't say, but low/mid elo he can easily dominate.
DO NOT build mulitple Warmog's or lifesteal on him. You open yourself to a cheap & easy counter(Execs Calling). What good is a build that is completely countered by a 1000 gold item?
Get a Warmog early - it is an amazing item on him, then support it. If you get a touch of armor and a touch of MR, you easily double or even triple his effective health. And he can't be countered completely.
Here is the build: http://www.leaguecraft.com/builder/D...3fd910afd30ffc
Sell the Doran's and upgrade the upgradables as needed. Easy 500 DPS with his spammable abilities, not adding cleaver damage(25% of their health), 7,800 effective health for 8,400 gold - usually reachable in a game. AND, not completely counterable.