I'll probably throw this up on leaguecraft once they incorporate Maokai, but here's what I'm running:
M: Magic Pen
S: Mana regen
G: CDR or AP (your choice)
I found that, being a support tank, you need a lot of mana and health. Combine that with some needed magic pen, and depending on your play-style, cooldown for more spamming or addition AP for harder hitting, you can hold a lane very well.
One point in Offense for improved Exhaust. Hitting all of the critical defensive stats, and boosting your Ghost and experience in Utility to help level faster and move quicker.
ghost + exhaust
That's why we got the masteries we did!
E, W, Q, E, E, R, then prioritize R > E > Q > W
Starting with saplings is a *must*. Already in 4 matches I've prevented a horrible clash in the bushes before the minions spawned because I was able to launch these little guys. And with no minions around, they'll chase after the champ guaranteed.
We get our next point in our root so we can help our lane mate safely damage an enemy, or, if an enemy is dumb enough to get too close to the tower, keep them there longer to take more damage. We'll ignore this for the most part until later in the game.
Our next point is in our Q. This gives us decent knockback, and is great for when you're being chased, or helping get enemies off a teammate.
At this point we have our combo. We root, then smash, then throw a sapling behind our enemy. After being rooted and knocked back, they'll run in the other direction, most likely right to the sapling for extra damage. I've gotten several kills early on this way.
After this, we prioritize our Ultimate (obviously), then our saplings for extra harass damage for the rest of the laning phase, followed by our smash to increase its damage output and assist in killing creep waves with our E, then our root.
Meki Pendant + HP
Tear of the Goddess
Boots of Speed
Upgrade boots: Merc Treads, Ionian Boots, Boots of Mobility, etc.
Randuin's or FoN (whichever is needed more against other team)
Randuin's or FoN (whichever you didn't already get) or Frozen Heart
If you are like me, you'll love throwing saplings all over the place during the laning phase. Mana regen is huge in helping to keep you in lane. Getting a Meki pendant won't solve the problem, but it'll help a lot until you get your Tear. The extra health pots will also help keep you in lane longer. I tend not to go back until I have enough to upgrade to a Tear, and also get a regrowth pendant and boots of speed. it is important to get the Tear quickly so we can take advantage of the additional mana we can acquire.
Warmog's is amazing on Maokai. With your smash and saplings, you can take down entire creep waves very easily. If you drop a sapling directly on the three mage minions, by lvl 3, it should explode killing them all instantly, and your smash should be able to take care of the melee minions in quick order. With Warmog's increasing your health, it helps with your passive which heals you for a %age of your max health. The more max health, the more healing.
Getting a Randuin's or a FoN helps keep you alive. Randuin's is great for the active, which will keep enemies in your ultimate a little longer in a team fight. The additonal movement speed and health regen of FoN is critical since you are pretty slow (even with lvl 2 boots).
Upgrade the Tear to an Archangel's staff. Now we're getting some additional AP to beef up our ultimate. Aegis is great for giving your team a little aura of happiness during team fights and in your ult.
The final item is really up in the air and depends on the situation. More defense if you need it (get a Randuin's or FoN - whichever you didn't get yet, or a Sunfire Cape so you can deal damage nearby and look like an awesome burning tree at the same time), or AP (Evil Tomb seems like a good item, or a Deathcap).
This is the build I have been going with thus far and have been doing fairly well with. I'm averaging 4 kills, 1-2 deaths, and 16+ assists a match. I'm also not very good, and not very aggressive, so results may vary.
Aggressive Build: (still toying with this, haven't actually tried it)
Sapphire Crystal + HP
Rod of Ages or Banshee's (whichever is needed more)
Deathcap or defensive item
This focuses more on putting the damage down and less on survivability. You'll most likely want another tank on your team if you plan to go this route. We're looking to gain the health benefits from Rod of Ages and Rylai's, the extra mana from Rod of Ages and Frozen heart, the cooldown and the AoE slow of Frozen Heart (along with the slow from Rylai's when you attack), and the extra AP that comes along with all of the items.
tl;dr; - you're going to make everyone around you really slow and dish out damage, but you're not going to be as tanky as you could be, so make sure you have another tank (or pseudo-tank) on your team.