Maokai being fairly new at this time is still seeming powerful and destructive. He can be a true beast it out with no problem tank or pure rape and destruction Ap caster. the item build is left open after boots because it really depends on your team chemistry and the opposing team.

Pros

Farmer
Early lane rape
Defensive Beast
Great initiator
Ultimate = win team fight
Great harassment

Cons

Slow
Focused easily
.....thats about about it

Now the runes pretty typical

magic pen marks
Greater Seal of Vitality health per level seals
magic resist glyphs
movement speed quints (because trees are slow)

I feel whatever you want to use is fine i would suggest mostly tanking or caster minions.

I go 9/21/0 for the masteries because again he is a caster tank, the magic pen is good as well as the tanking masteries.

For the items start with Doran's for mana regen and the Ap (health pot optional)
then i get the "Tear of the Goddess" and basic boots on my first back. Next is generally "Mercury Treads" .

Ability power build

Rabadon's -> Zhonya's -> Abyssal Scepter and whatever seems good, usually play it by ear a tanking item such as Banshee's Veil couldn't hurt or Guardians

Tank build

Frozen Heart -> FoN -> again Banshee's Veil well you get the idea if your thinking of tanking you should know what to build to your situation. Thornmail if the opposing team is heavy physical and basic attack based.

I get the toss for obvious harassment, then level two becomes rape mode this is where Maokai shines. Level two you get the stun , and can go rape mode. you can kill any relatively squishy champion solo with enough harass and even the tanky champion with help, I recommend Ryze . Well anyhow maxing Sapling Toss and Twisted Advance first is what I do getting his ultimate when available.

For summoner spells i like clarity for early game harassment and sustaining his ultimate throughout the game and ignite is always nice especially for the early game rape phase at level two.

Optional
Ghost
Teleport
Fortify
Whatever you like and are comfortable with I'm not playing for you.

Early game/ Lane phase

I like to start with the Sapling toss for obvious harassment and minion farming. Once you have toss level 3 you should be able to one spell "2 hit" landing and explosion the caster minions. however form level one i like to harass the champions and hope by level two they are half health and sticking around or at least out of hp pots , at this point you want to coordinate with your lane partner hopefully with another stun and then target the weakest opponent, you sapling toss then twisted advance and your teammate follows up with some damage and their own stun and the target will hopefully be dead if at least backing and leaving lane.

Mid/Late game /team fights

Lane if you prefer or start ganking with your team either way you should be pretty indestructible with your team and ult around. When the team fight starts going down yuo first instinct should be "R oh my god R!" Vengeful Maelstrom , proper placement of this is crucial and can easily turn the fight. At this point with the tear i can almost leave this up without noticing it until the end of the fight especially with clarity it is very easy to keep up, just remember it can do a fair amount of damage so if the fight is winding down blow it and hopefully seal the fates of the opposing team.

If you find yourself ganking you can do two routes pending on who the target is if the target is squishy and easily killed open with twisted advance to gain the early ground, otherwise use it to corral the runners, Tryn , Kassadin
etc...

In conclusion Maokai is an awesome champion whether you go tank or caster and can dominate any game. He is very versatile and and swing many games either way. I enjoy this addition the the champion roster and enjoy playing him in both fashions he is great for saving your team or initiating the destruction of the other team. If you vote please leave a comment it is not required.