So, this is my Mundo tank build. I have used this build MANY times and it's what works best for me and my play style. My main motivation for making this guide was the fact that I have seen too many Mundo's fail, and fail at their item builds. I die a little inside when I see this happen. This is the best Mundo build out there(in my opinion), in regards to tanking.

Pros:

Amazing survivability.
Decent damage, even as a tank!
Decent farming ability
Enough damage to kill people!

Cons:

Heal lessened by Ignite(But still not a hard counter in my book)
No strong CC
Can't technically tank because of lack of tanky CC.

Why did I choose these particular runes?

Well, I chose Greater Mark of Fortitude's for the straight up health right off the bat!

The Greater Seal of Evasion's are a very important decision in my opinion. Personally, I'd rather have dodge than more health. Why? If I can dodge an attack, I take NO damage. So, if an attack hits for 100, and I dodge it, that's 100 damage I don't have to take. If I have the health seals, and get hit for 100, that's damage taken away from my health, and probably not as much as I got from those seals. I have also been saved many times by dodges, where if I wouldn't have dodged the attack, I would've died right there. They're lifesavers!

The Greater Glyph of Focus's aren't really all that important. You could substitute whatever you want here, really. I just like being able to throw a cleaver every 3.7 seconds :D

So, the defense tree is a must for tanking, obviously. I like putting the other 8 in utility because I feel the extra experience and extra health regen it gives you help you out. You'll be able to get level 6 faster, not by that much, but it could be enough to save you.

Time to explain my items!

CORE:

Doran's Shield - Get this first, because it gives you some nice regen for staying in the lane, even under constant harassment. The extra armor is also very nice, as well as the health. Combined with Mundo's passive, it's a nice starting item.

Ninja Tabi - Along with the dodge masteries, the dodge runes, and Mundo's general "bossness", you dodge a lot thus allowing you to stay alive! Somewhere around 25% dodge with everything, if I'm not mistaken.

Spirit Visage - A VERY important item in the build. In another build, they suggest buying this first, but I disagree. If you have boots, you can avoid some skill shots and with the extra dodge, may even dodge some attacks. You'll also move faster with boots. I buy this item 2nd, because of its passive.

Force of Nature - This is the 3rd item you buy. I buy this 3rd for a few reasons: Its passive, mainly, but it also gives you some nice regen and some magic resist. The extra movement speed is nice too! (420 with it, tehe) Usually, I sell the Doran's here to buy the Negatron Cloak if I don't have enough.

Warmog's - This item is 4th. I often see players get this first, and I don't understand it. Sure, you have more health, but without resists, it'll just take a couple more seconds to kill you. You NEED resists first. This is an important item, but get it later, not sooner!

Additional Items:

Sunfire Cape vs Thornmail - The enemy team comp should determine which you get. If they have a lot of auto attack carries, such as Gangplank, then get the thornmail. If they have someone who just does physical damage with their skills, or they don't have much physical damage, get the Sundfire Cape. Again, which one you choose is dependent on their team.

Guardian Angel vs. 2nd Force of Nature - This one is more personal preference. You can move fast with the 2nd FoN, or get a 2nd chance at living with the GA. If they have a lot of magic damage, I would go with the FoN. If they have more physical, go with the GA. If they're even, feel free to get whatever you want!

Ghost - This is a MUST for any Mundo build! Why? Because combined with your ulti, you can almost ignore the effects of exhaust or any other slow. It's also pretty fun to run around really fast lol. Crucial in escaping/pursuing.

Flash - This one fits my taste more as a second summoner spell. It's useful for staying alive, and even flashing on people with your Burning Agony on to get that last hit, and making it easier to cleaver them.

Exhaust - This is another viable option for Mundo. I used this for a little bit while playing him, and it was actually a decent spell to use on him. Helps pursue, and get away, while minimizing damage on you. You'd use it exactly like you would use it on any champ. Pretty self explanatory.

Ignite - Not one of my favorites on Mundo. I don't really see the point of it. I know I can get just as many kills without this skill and stay alive longer with another skill.

Cleanse - Not sure how well this works on Mundo. I've never used it. It seems like it would be a decent skill to have, but I can't be sure.

Any other spells - Meh. Do what you please. I'm just telling you which skills work best for me.

Well, I'm kind of ashamed to say this, but I've only played 1 ranked game, ever. I did play Mundo in it though, and I did decently well. Of course, I can't take all of the credit. My team certainly helped :)

I don't really have a problem with Ignite. Early game it can kinda hurt, but even late game, Mundo isn't affected by it all that much. Sure, it cuts your healing in half, but you should have enough survivability by then to just wait until it's over with. If the other team is smart, they'll wait until you pop it to use it on you, but even then you get half of that. You end up with about 4k health at the end with the full build, and even then your ulti should be able to heal through quite a bit of damage.

Well, this is my modest guide to Mundo. It works damn well for me, and I love playing him. I can't tell you how to play him though. I can only tell you what works best for me. Also, I apologize for the looks of this. This is my first build on here, and I don't know all the little tips and tricks for making it look nice. Any feedback is appreciated, whether it be negative, or positive!