Mundo is a great champ. He's very tanky, slows his opponent and to take the cake regenerates health super quick with is ult.

I always get dorans shield first. the extra health and health regeneration is worth it.
by mid game you should have Warmogs Armor, so you will be pretty tanky.
some might question the phantom dancer and boots of mobility combo to be a stupid one, but i tell you it isn't. Dr.Mundo is already one of the best chasers with these items he can catch anyone.

Pros

Great health
Great movement speed
Amazing attack with/masochism

Cons

If your against a heavy AD team you will do poorly unless you build Thornmail