This is my first build guide, so I would appreciate any tips on making it better.

This is how I build Maokai, and, depending on how the game goes, you will be able to pretty much destroy anyone without damage items till mid game. Built like a tank, he can still be a great tanky dps. Even if you aren't out there "hugging" everyone, you'll still be an excellant tank.

My catchphrase when playing him: "IN SOVIET RUSSIA, TREE HUGS YOU!"

This build is for those who want to tank Maokai. He is quite viable as an AP caster but this guide doesn't cover that bit. To start off, I'll describe the role of a tank.

Soak up damage
Protect squishy allies
Initiate teamfights
Get focused
Deal supporting damage
Help disable high-value targets

Despite everything you have to do, being a tank isn't all that hard. In teamfights, you are the one to go in first, you are the one who should outlast most other combatants*, you are the reason the ranged carries, assassins, and supports can do as much as they can in a teamfight. Without a tank, your team loses a good portion of their teamfight potential, because they will die a lot faster without a wall in front of them.

*If you are the first to die in a 5v5, you need more survivablity. If you're still the first dead, congratulations. You have saved your team from 10000 points of damage.

BUILD SUMMARY
Mercury Treads - Tenacity, early MR, Speed
Banshee's Veil - Spell Shield, MR, Mana
Thornmail - Armor, Damage Return
Rylai's Crystal Scepter - Health, AP, CC
Force of Nature - MR, Speed, HRp5
Pick one

Atma's Impaler - AD, Armor
Sunfire Aegis - Health, Armor (sub Thornmail)
Abyssal Mask - MR, AP, MR reduction
Guardian Angel - Armor, MR, Revive (sub Thornmail)
Randuin's Omen - Armor, Health, AS debuff, Slow (sub Thornmail)

For details, see below

My item build changes as the game/enemy team changes. I don't have a specific component order as I dont decide until the game starts which item I start with. Remeber, tank builds need to flow with the game.

Early game:
For my first items, I'll grab 1 of 3 sets, taking into consideration who I will be facing in the lane

Cloth Armor, 2 health pots, 2 mana pots - Mostly physical damage (Tryndamere, Caitlyn etc.)
Null-Magic Mantle, 1 health pot, 1 mana pot - Mostly magic damage (Janna, Karthus, etc.)
Ruby Crystal - 1 of each above

Next I will get boots, upgrading to Mercury Treads if possible. After the boots, I start on Thornmail ( Cloth Armor) or Banshee's Veil ( Ruby Crystal, Null-Magic Mantle (after Treads)). If you decide you don't need Thornmail, this is when you'd buy the armor item of your choice. My recommendation would be Randuin's Omen, especially if you find yourself against AS *****s. If you don't have enough money for an item, get potions according to your needs.

Mid Game: Once I'm done with the first 3 items, I start building the Rylai's Crystal Scepter. I get the most expensive item possible at the time first, then continue to build. If I end up with a Tome and approx. 550 gold, I'll sell it for the Wand. Once Rylai's is complete, start on Force of Nature. You should have 2 slots left at this time, so you should get a Negatron and 1 Pendant before you have to complete it in one buy (1435 gp)

Late game: Your last item can change depending on what you need. For AD go Atma's Impaler, as the huge amounts of health you have will give you a great boost. The armor is an added bonus. Sunfire Aegis will give you a good health and armor boost, as well as a little bit extra damage in big teamfights. If you aren't facing a lot of AD, this can replace Thornmail. If your team has a lot of AP or you need some more MR, AP, or both, take an Abyssal Mask. This will give you an excellant amount of both AP and MR, and is a great supporting item for a largely AP team. If you find yourself dying in the middle of teamfights a lot (which you should be), grab Guardin Angel. This gives a nice boost to your armor/MR, and the passive is infinetly useful for continuing in teamfights. This can also replace Thornmail. Finally, we have Randuin's Omen. I wouldn't recommend getting this as your last item, as it is as good as or better than Thornmail at disabling AD carries, so you won't need it if you get Randuin's.

If you find one of these suits your needs more than one of the core items, use it. Tanks need to resist the most common damage source.

For most champions, there is usually 1-2 more used skills and 1 less used skill that is neglected. For Maokai, all his skills are necessary in different ways. This section details what they are, as well as when and how they should be used.

Arcane Smash (Q): Skill shot slow, deals damage and knocks back enemies in an AoE around you
Uses: Great farming, useful CC and disruption, ABSOLUTLY NECESSARY when running from melee champs.
Combo with E to clear a minion wave (or 3) in seconds, or with W to disrupt ultimates quickly. Invaluable when running, the knock and slow make it hard for most champs to stay on you. However, the short range severely limits use against range champs.

Twisted Advance (W): Jumps to target enemy, then snares for a few seconds
Uses: Initiation, saving allies, Saving Private Ryan, chasing, and imobilization for AoE/skill shots.
I take this first because of its chasing power, very useful in an early skirmish. It also helps to keep an enemy inside your R, and will save a low health teammate from most chases. It almost forces an enemy to focus you, which is the main job of a tank.

Sapling Toss (E): Tosses a sapling to target location, remains there for up to 90 seconds. When an enemy approaches, or the time is up, the sapling explodes and deals damage.
Uses: Bread and butter farming, harrasing, scouting, and nuking.
These little guys are the easiest way to earn money, because at max rank they can destroy minion waves all on their own. With a Rylai's, the become excellant CC and more likely to hit both times. Be careful of positioning though, as enemy minions might deny you a kill or harrass. Take this first if you need harrass more than you need a jump/snare. In that case, swap this and Twisted Advance.

Vengeful Maelstrom (R): An AoE nuke that absorbs damage in radius, when it activates again or you run out of mana, it explodes and deals damage based on what it absorbed.
Uses: Protecting team, AoE nuke, counters enemy AoE ultimates, jungling large monsters.
A powerful nuke in the middle of a teamfight, but you have to be careful of when and where you put it. You need to get as many players on both sides in the ring as possible to max its effectiveness, and is near useless in a moving or spread out teamfight. However, it is quite useful when you do use it, as it has both defensive and offensive properties. It can even be used in suicide charges, though not recommended when that would give the enemy an ace. When goin for Baron, definetly throw this up to keep everyone healthy in case of a gank.

I use:

Heal - save allies and stay alive to keep tanking
Exhaust - stop chases, aid in chasing enemies, and with mastery, mark target for takedown

Also useful:

Clarity - If you have mana problems (almost guarentee you will)
Cleanse - You won't be doing much tanking while under CC
Teleport - Save the squishies faster, as well as defend a turret under attack
Flash - Need I say more?
"Surge"* (new spell) - Helps team, great because you'll always be in the middle of everything

If you use one of these, make sure you get the appropraite mastery (if possible).
Meh spells (keep in mind that you're supposed to stay in the middle of a fight):

Ghost - Speed isn't necessary in middle of teamfight, and you'll have enough once you get Force of Nature
Revive - only useful in end of game when you are losing. Don't plan on that happening
Clairvoyance - you should be tanky enough to survive a jungler gank, let someone else get it
Ignite - nice damage, but you shouldn't be the one doing the damage (even though you will be)
Smite - Even though your a tree, you shouldnt be in the jungle. Teamfights excluded, and you won't be using it then.
Promote* - You won't need a superminion help when clearing waves


*These summoner spells don't exist in Classic mode yet, but are being reintroduced soon. Fortify and Rally have been left out because they are being removed. As this guide is not for Dominion, I have not included Garrison.

These runes are not exactly what I have in game. They are (in my opinion) the ideal runes for tanking. They provide the 3 essential tank stats of Health, Armor, and MR; all at early levels. If your early game is consistantly easy on you, you could switch to "per level" versions for more late game tankyness

Other useful Runes

Greater Mark of Magic Penetration - If you want to deal more damage, this is the best way to do it.
Greater Seal of Mana - A whole set will give you an extra sapling or snare.
Greater Seal of Scaling Mana Regeneration - I don't really like these, but the extra 10 Mp5 once you're 18 may be helpful to some.
Greater Glyph of Scaling Magic Resist - Another good option for MR, these are the ones I'm currently using. A 4/5 mix of Shielding and Warding runes will give you a nice balance of early and late game MR
Greater Quintessence of Ability Power - Another option for more damage.

Most of these options are for a more AP-nuker build. If you want to tank, don't take more than one of these as a full set. Exception for Greater Glyph of Scaling Magic Resist.

Thank you for reading my guide, and please give me your honest opinion on it. Internet Trundles, I encourage you to flame my guide as long as you don't downvote it. Your comments are usually hilarious.