This Mundo guide/build will result in a mundo with extreme amounts of health resulting in being almost unkillable especially when using your ultimate.

Warmogs Armor - Do i even need to explain this one? HUGE amount health and well worth the price
Merc treads - Good CC reduction
Spirit Visage - Works well with ulti
Frozen Mallet - Has health, a bit of damage, and a nice slow
Sunfire cape - Health plus 40 dmg a secound nice when paired with burning agony
Randuins Omen - i just kinda like this item seems to work well chances are you wont even get to this item before the GG

I find that Ghost walk and heal work well but flash,Exhaust, and Ignite seem to work nicely too

I find that for some reason tanks dont seem to use their HUGE amounts of health to their advantage when it comes to turrets, Simply just walk up to the turret u want to kill with another champion (since you cant hit turrets very hard) make sure you are taking the hits, use masochism and boom turrets gone in no time at all great for quick pushing sicne you dont have to worry about creeps to tank for you. Also dont be afraid to turret dive (late game NOT EARLY GAME) you shrug of turrets hits like bullets hitting the incredible hulk.