Build for mundo, I don't play TT myself, I start with dorian's shield if I'm jungling, or regrowth pendant. Next I get boots 1, spirt visage, warmogs. Boots if there's tons of cc merc treads are okay but not needed, typically Ionian or speed 3.
That's standard first 3 for any mundo. Next its sunfire for me, since I'm MPen, if your playing physical get atma's. For mr I use Abyss scepter 60% of the time, if there's a high magic threat from madrid's, or a ap player FoN is far better, but I focus on magic damage, so 12 extra aoe damage a second and mpen makes me nasty.
If there's a yi/olaf/renek/tryn/ashe etc high threat physical get thornmail or abyss/fon if its magic.
My deadly ap build where there's plenty of tanks.. And people talk trash until I'm 25/5 k/d is
Spirit visage, warmog, abysss scepter, hourglass(armor high ap, and you can phase out), void staff or deathcap.. Burning agony does INSANE damage..
The thing about burning agony is it reducess CC effects when on, you charge in? Turn it on when you expect to get nailed and stunlocked!
Never forget mundo's ABC's of success.... Alway's B Cleavin!(Corporate mundo)
Mpen makes cleavers deadly, and burning agony, ult whenever ur under 80% hp and don't expect to need it soon. Ap only boosts burning agony