Welcome to my second build. This time, the incredible tank, Maokai. First thing's first, Maokai is most effective in the lane, with a partner, specificially one who casts many spells. I do not believe in Maokai's purpose being a jungler. As with my Anivia builds, I'm not intending to make a tried and true, ultimate, competitive build. I'm a pretty casual LoL player, as far as League players go. While there're many, many ways to play Maokai, I fall somewhere between tanky AP, and a pure tank. I've tried numerous builds with him, and I think I've finally found one which works wonders. One final note, it's important to realize that Maokai's main job is not to take the feed, but to protect the team, and get them fed whenever possible. I've tried playing him as a pure tank, but he falls off late game, and I don't find it to be worth it. Without a taunt, Maokai's difficult to be played as a pure tank. The good news is that he hurts pretty bad for someone so tanky.

I appreciate constructive criticism, however, don't waste your time commenting if all you're going to do is complain about how I'm not following the meta, or something equally pointless.

As previously mentioned, I tend to play Maokai somewhere between tanky AP, and a pure tank. I take mostly defensive runes. As a tank, your main goal is to protect the team. Once (or rather, if) you have a full build, you want the turrets to tickle. You should be able to tank them without many minions, and allow your team to crush the towers without having to worry about taking damage. Maokai is tied (with Poppy) for having the highest natural armor of any champ in League of Legends. Between this fact, and his passive, he's set up to be one hell of a tank. For his runes, I recommend getting as much defense as possible, while getting just the right amount (I mean it, these quints can easily mean the difference between a kill/assist) of extra movement speed (MS) on the side. You wanna be able to catch the target with your W, Twisted Advance, which can lead to some truly EPIC ensnares. If you do, your team has a golden opportunity to eat the victim alive.

Explanations
Greater Mark of Armor: Even though Maokai has the highest natural armor in the game (tied with Poppy), extra armor can't hurt. Especially since as the tank, you're goal is to try and take all of the damage that you can. This makes doing that easier.
Greater Mark of Attack Speed: Since I typically play Maokai on TT in a manner I call "psuedo-jungling," I now take these marks over extra armor. The simple reason is because I spend a decent amount of time in the jungle, and these greatly increase your clear time, which allows you to get to the next desination quicker, and making you take less damage overall.

Greater Seal of Armor: These're probably the best seals in the game. As explained above, every bit of extra armor helps, especially on a tank, since you're gonna be trying to take the hits.

Greater Glyph of Scaling Magic Resist: The above runes're for armor, while these're for MR. Since mages have to build their damage from closer to scratch, you should use that to your advantage and get the full, per level MR runes. Don't worry about getting AP, such as Greater Glyph of Ability Power, since your main goal isn't to hurt people.

Greater Quintessence of Movement Speed: You wanna get Twisted Advance off as often as possible. MS makes this easier, and these quints give you that. Again, your main goal isn't to hurt people, so don't concern yourself with AP, CDR, or anything of the sort with runes.

Maokai's Masteries're also easy to describe. He's a tank: build heavily in the Defense tree. I LOVE improved Ghost in general, especially on Maokai, who needs to catch enemies with his W. Since I'd get Summoner's Wrath just for the improved Ghost anyway, it's lucky that Exhaust is improved with the same mastery, since then that spell's improved as well. Using Utility as the secondary tree, you get some very welcome extra mana, mana regen, a slight increase in MS, and a generic "spend less time dead" ability. It's nice for if and when you die, and since you need another point to get the second tier of masteries, it's useful.

Explanations
Summoner's Wrath : This improves both of your Summoner Spells. Since improved Ghost is worth taking this mastery for alone, it's obvious when you consider that it improves your other Summoner Spell, as well.

Resistance : You're a tank. MR is part of being a tank. This gives you MR, and gets you in the Defense tree.

Hardiness : You're a tank. Armor is part of being a tank. This gives you armor, and gets you in the Defense tree.

Durability : Health is part of being a tank, as well as augmenting your passive. You're a tank. I trust you can figure this out.

Vigor : This gives you some more health regen, and allows you to get deeper into the tree, so this is a very welcome addition.

Veteran's Scars : Not a huge bonus, but it helps for the first couple levels, and more health is never a bad thing, especially when you wanna be taking the hits for your team.

Initiator : This is helpful for ganking. Since you're gonna have a ton of health by the end, it'll take more to get you below the 70% health mark, so you'll get more out of this than squishier champs.

Enlightenment : CDR helps Maokai litter the area with saplings, as well as makes sure that your W's ready at all times. Since Maokai's usefulness comes from his spells, you can't go wrong with CDR.

Juggernaut : More health and essentially stackable tenacity? Count me in. This is perfect for Maokai. Plus, if you don't get Mercury's Treads, you'll still get some form of tenacity. Or, if you do get them, you get even more tenacity. The less time you're busy being stunned, the more opportunities you have to assist the team.

Good Hands : Since you don't need Summoner's Insight , and you need a fourth point in Utility to get deeper into the tree, this is your best bet on spending that point. It'll make you respawn quicker, spending less time dead, and more time defending/assisting.

Expanded Mind : Even if Maokai isn't a heavy damage dealer, he's very mana hungry, and this mastery gives you some extra mana. It's very simple.

Swiftness : This makes you just a slight bit faster, but any extra MS is very, very welcome on Maokai. Getting that W off and being able to get where you need to be in order to defend are essential points to playing Maokai, and MS makes them easier.

Meditation : Mana regen is very nice on Maokai since he's so mana hungry. It helps, especially since you won't be getting a Philosopher's Stone. You could put these points into Swiftness, if you'd prefer, but I think that I put enough extra MS in the build to justify the extra mana regen, however, I may change it around, and remove these points to max Swiftness out.

Stay tuned for major changes once season 3 starts.

*Obviously, you'd only get one pair of boots. Choose which pair based on how the enemy team looks.*

Maokai is a very situational champ. As a tank, he needs to be aware of how the enemies are building themselves. This is first noticed when deciding on which boots to get. You could go for Ionian Boots of Lucidity, since Maokai benefits heavily from CDR, but again, your main goal isn't to hurt people, so I recommend Mercury's Treads or Ninja Tabi. Maokai is tied (with Poppy) for having the highest natural armor of any champ in League of Legends, and I have extra armor built in with runes, so don't be afraid to get Merc. Treads almost purely for the Tenacity if the enemy team appears to have a ton of CC. Following this item build, you'll actually build some damage while becoming tankier. Plus, once you get Rylai's, you'll help slow enemies, which adds even more CC to help with the assist master. The items listed up at the top're general items which you should probably get every match, if possible. After these, I suggest the following, based on what the enemy team looks like:

AD-Heavy Team: Thornmail, Frozen Heart, Randuin's Omen
AP-Heavy Team: Force of Nature, Spirit Visage, Abyssal Mask*

*If both teams're caster-heavy.

Force of Nature (FoN) is so good, that I suggest getting it unless the enemy team's damage is literally all AD. Aside from providing plenty of magic resist (MR), it gives you an extra boost of MS, (which is very nice for getting your W off) and gives you INSANE health regen. Not only does Maokai have a pretty high natural health regen, but his passive also heals for a percentage of his max health (which, following this build, will be very high), combined with the passive on FoN, will make you extremely difficult to take down.

Philosopher's Stone: This is a very popular item for support/tanks, however, I've used it many times, and I don't recommend it. It's nice that you can use it to earn some gold, then finish it off at the end of the game into Eleisa's Miracle, which gives you nice tenacity and regenerative bonuses, however, it's 800 gold, near the beginning of the game, and I just don't find it to be worth it. Working on Catalyst the Protector early provides extra mana, which I find almost as helpful, especially early game, and that item soon becomes a Rod of Ages, which is very useful. Also, if you get a Philosopher's Stone and Merc Treads, upgrading the stone would render the tenacity obsolete. So, you'd either have to change your boots to Ninja Tabi, or sell the stone, which takes 26 1/2 mins to pay for itself.

I suggest taking Ghost and Exhaust for Maokai. Both of these'll make getting your W off much easier, which, if you haven't gathered from this guide yet, is one of the main goals of Maokai. These're fairly self-explanatory, so I won't get too in-depth to them, but the main idea is that you don't wanna allow anyone to escape from your team, and both of these make doing that much easier. Also, these help you in assisting your teammates from dying.

Ghost: A huge boost of extra MS, which is very nice for getting your W off. (If you're sick of reading that over, and over, and over, I apologize that you're being punished for actually reading the whole build, but apparently, some people're commenting without reading what they're talking about, so I'm putting things in multiple times. Again, I'm sorry.) This is useful for both ensnaring enemies to have your team eat them alive, and halting them in their tracks to stop them from chasing your teammates.

Exhaust: This, along with Ghost, makes it easier to chase/escape from opponents, which makes getting your W off even easier. If that means nothing to you, you CLEARLY haven't read the rest of the build.

First of all, I do see how Maokai could be a viable jungler. His passive heals him, and he can pack a punch if you build him in such a way. Also, his W, Twisted Advance makes for a nice gank coming from the jungle. I'm not trying to advocate that Maokai can't jungle, simply that having Maokai in the lane is extremely underrated.
A. Maokai's a tank. A jungler should be more focused on damage. While Maokai can be built to really hurt, he falls off late game in terms of damage. He simply can't carry. If you build Maokai for damage early by jungling, he won't be very useful late game.
B. Maokai's passive works most effectively when around other champs, especially if your teammate (who you could defend by being in the lane with them) casts numerous spells. Although Maokai's passive could be useful for keeping him alive in the jungle, he's a burst champ, and a jungler shouldn't NEED to use their abilities to clear the jungle, especially one as mana hungry as Maokai. Even with blue (buff), Maokai needs to wait to regenerate his mana. Even with his passive, that isn't a ton of healing. Most junglers get lifesteal very early, and they're healing a lot more than 7% of their max health much faster than every 5 spells and a basic attack.
C. Maokai can't solo. Period. He doesn't hurt enough. If he encounters the opponent's jungler alone, he can't do much to fight back. Your jungler should be able to strike fear into the enemy jungler, not let them most likely get a free kill. Even if they don't kill Maokai, he'll most likely have to run, as opposed to killing them.
D. Consider that jungle Maokai is best when he pops out of the jungle and ensnares an enemy with Twisted Advance. If Maokai's busy jungling, he won't be able to get as many ensnares off as if he was laning. While he may not have the element of surprise, he more than makes up for this with his harrass. He has one hell of a harrass spell. His E, Sapling Toss is absolutely amazing for harrassing and pushing. It does a ton of damage (up to 460 + 100% of your AP), CHASES the enemies (even if the minions can get in the way), and due to this, it has nice zoning capabilities. They simply can't ignore it, it just hurts too much. Not only this, but it grants sight, AKA, it can be tossed in a bush to see if any enemies're hiding in it. Saplings only last for 35 seconds, however, they can be used as slight substitutes for a ward, in some situations.
E. Maokai's ult is purely for team fights. Assuming he's jungling, he'd pop out of the jungle for a gank, and the enemy's gonna try to run away. Since Maokai's ult is used on an area, this renders his ult practically useless for the first major portion of the game.

*Obviously, you'd only get one pair of boots. Choose which pair based on how the enemy team looks.*
This section can be confusing above, so please read.

For the first couple of items, I don't intend for you to buy everything. You'd only follow one path, and only get one pair of boots.

Mainly for the items, I'm still working this section. I've tried a couple of different items for Maokai on the new TT, and so far, I've had the best luck with these items. I really think Hextech Sweeper could be good on him, but I always do poorly when I get that. I still recommend Force of Nature, and actually, Wooglet's Witchcap isn't bad for him if you need some more damage, since new 3s is more based around offense now, and because it grants a nice boost to MS.

Ironically, Maokai is an incredibly jungler on the new TT without sacrificing his tankiness, or the integrity of my build. The one difference is that I've switching my marks over to Greater Mark of Attack Speed, to help with jungling speeds. By following my build, you only lose out on a little armor, and get a stable income and exp without taking anything from your bottom lane. Since the jungle is realatively small, ganks are easy, and you aren't ever very far from either lane if one of your teammates need you.

Situational Items
Anti-AD: Thornmail, Frozen Heart
Anti-AP: Force of Nature
Extra Damage: Wooglet's Witchcap

OP'd: Overpowered
AD: Attack damage
AP: Ability power
MS: Movement speed
MR: Magic resist
CD: Cooldowns
CDR: Cooldown Reduction
AoE: Area of Effect

RoA: Rod of Ages
TotG/Tear: Tear of the Goddess
AAS: Archangel's Staff
Deathcap: Rabadon's Deathcap
Rylai's: Rylai's Crystal Scepter
Warmog's: Warmog's Armor

TT: Twisted Treeline
SR: Summoner's Rift
3s: 3vs3; Twisted Treeline
5s: 5vs5; Summoner's Rift
Old 3s: TT prior to the total remodel on 10-25-12.
New 3s: The current TT, with Vilemaw, new items, etc.

IMO: In my opinion

If there's anything I missed, please let me know.

Maokai is an incredible, versatile tank. He becomes incredibly difficult to kill late game, while making it very easy for your team to devour enemies thanks to his Twisted Advance. For such a durable tank, he also hurts quite a bit. While he could never carry, that isn't his job. He gets good without stealing the feed, but instead, provides it for his team.