Wanted some help in learning how to build Mundo, those experienced with him: Could I get some insight in as to what you guys build on him?

Thanks!

Doran's Shield, Mercs/Ionia/Bers, Spirit Visage, Randuin/Sunfire/GA, Force of Nature, Stark's, sell Shield for whatever - Infinity Edge for more damage, either GA or Sunfire for defense, whichever you didn't buy before.

stack 6 warmogs, you will win every game

Mundo don't care bout build, mundo build what he pleases

Dr Mundo rules the WORLD as he pleases

Must have item: Spirit Visage
Pick One: Frozen Mallet or Warmog's
For Damage: Stark's, Ghostblade, Black Cleaver
For Armor: Atma's, Randuins
If Magic Heavy: Force of Nature
Boots: Merc Treads or CDR boots

Don't make Warmog's.

Runes

Quints - Armor Penetration
Reds - Armor Penetration
Yellows - Health per level or Dodge Chance
Blues - Flat Magic Resist or Per level Magic Resist

Masteries

0/21/9 - This is for your standard tank Mundo, Get tank masteries in defense, and in utility get the improved HP regen, ghost (if you use ghost) and EXP boost.

21-0-9 - This is for AD mundo, Get standard carry masteries in offense, and in utility improved HP regen, ghost and EXP boost.

Build

Get Dorans shield first, secondly get a spirit visage, and this is where you build differentiates if you're playing AD or Tank.

I usually build him as a Tank/DPS, Getting items like Atma's, Sunfire cape, and Starks. Otherwise I get Randiun's omen.

Skill Order

For AD, max your E first.

As Tank max your Q first.

As Hybrid Tank/AD get Q First, and max E afterwards.

Mundo builds how Mundo pleases

I've never been much for Mundo myself, so instead I shall do this: http://runeterra.com/forums/index.php?topic=33.0

There's a bit of discussion about Mundo on this thread regarding summoner spells, masteries, skill orders, items and runes.