Pros:
- Dr. Mundo has the biggest health regen in the game!!
-His spells cost health, not mana.
-At early game Infected Bonesaw are good for damage, at late game for their slow.
-Mundo has a massive damage from Blunt Force Trauma.
-Mundo can easily take down dragon or baron, because Infected Bonesaw's damage is based on the enemy's health.

Cons:
-With an Ignite, his ult doesn't regenerates anything...
-His Infected Bonesaw stops at the first target, so if you play against mundo stay behind your minions!
-In early game Heart Zapper costs too much health.

ALWAYS start with a Doran's Shield. It's very good for you: health, regen, and armor. At the first recall buy your boots: Mercury's Treads or Ninja Tabi. Your next item will be the Spirit Visage. It's extremely important, improves your stats, passive, and ult too!! If there is a full AD team against you, you should buy Thornmail for next, and if the enemy is full magic, you should buy Force of Nature.
If the enemy team is balanced skip Thornmail and Force of Nature, and buy a Warmog's Armor. Next Sunfire Aegis, it's good at high level with your Heart Zapper. You can buy another Warmog's Armor (it hasn't got UNIQUE Passive, so you can stack it...). Then buy a Guardian Angel for teamfights.

Other good choices:
- Banshee's Veil: It is also good against casters, but not the most important for Mundo.
- Randuin's Omen: Very good item: great survivability, and an AoE slow. Good at teamfights.
- Atma's Impaler: If you have 2 or more Warmog's Armor, you MUST buy this item. gives armor and a high damage boost.
- Frozen Heart: Most tanks buy Frozen Heart, because they haven't got any mana. Mundo doesn't uses mana, but Frozen Heart is a good choice against strong AD teams.

When your whole enemy team is AD carry and tank, you MUST have a Thornmail! Spirit Visage is not as important as in other setups, so in the early game you can buy that, but in the late game armor items like Frozen Heart, or Randuin's Omen are more important.
Start with a Doran's Shield. Then buy your Ninja Tabi, or if you play against a lot of CC-er, you can buy Mercury's Treads. First buy a Chain Vest, and if you reach 1300 gold turn it into a Thornmail. Next item should be Sunfire Aegis, or Warmog's Armor.
Sunfire Aegis maximizes your damage, and Warmog's Armor maximizes your main stat Health regen. I you buy Warmog's Armor first, your next item will be Sunfire Aegis, and if you buy Sunfire Aegis first, the next will be Warmog's Armor. For your last 2 items you can choose from: Guardian Angel, Frozen Heart, Randuin's Omen, Infinity Edge, Atma's Impaler. In 5v5 you should choose from Guardian Angel, Randuin's Omen, and Frozen Heart. In 3v3 you can buy offensive items, like Infinity Edge, or Atma's Impaler. And you can buy more Warmog's Armor, for health, and health regen boost!

A little bit harder than the Attack Damage build. The core item in this build is Force of Nature, it doubles your passive, and gives a LOT of Magic Resistance!
Basically, your first item is Doran's Shield, and next is Mercury's Treads. The third shoul be Force of Nature: if you are in a big trouble from the strong enemy casters like Malzahar or Brand, you should buy Negatron Cloak first, and if not, you can buy the Regrowth Pendants before Negatron Cloak. Next you should buy your Spirit Visage. After that you can buy Banshee's Veil, or Guardian Angel, or Warmog's Armors. At the end you can buy offensive items too, like Infinity Edge, or Atma's Impaler.

I use and . I don't say this is the best or the only good choice. With you can catch enemies and you can easily run away from 1-2 enemies. With + . you can escape from the whole enemy team. I think is a great choice too, often I use for 3v3. + combo is fckin good!! You can use to maximize your damage, or .
is also perfect at teamfights.

Dr. Mundo's most important spell is Infected Bonesaw, so you should learn it first, and max it first. Some Dr. Mundos learn Heart Zapper for their second spell, but i think Blunt Force Trauma is a lot better because: costs less health (that's very important at early game, at late game you have very high health regen), and it gives you a bigger damage. But Heart Zapper is better for Jungling.