This is my first build so I know description wise this is a little weak but I'm mostly posting for the item and skill build. I've seen to many ap Maokais lose terribly to so many things.

Maokai has a very under rated passive. With HP and CDR + MP5 he can virtually stay in a lane forever. With his snare, slow, and rylais (in late game) there isn't a champion in the game who can get away. It's still very important that you don't run off and solo, teamwork is a MUST with his low damage output and fully team based ult. It is also always important to keep in mind that this build can always be changed according to the other team, if they run stun/cc fix the boots to mercs and if they have little to no ap ignore the force of nature.

I chose to level up the snare fully asap to allow for really powerful bush strikes and the rest going into his toss to allow zoning, very effecting warding, and with mp5 and cdr i can use my passive to stay in a lane forever. If you are getting ganked a lot than put 1 point in to your toss so you can ward bushes and the rest is to slow anyone that tries to chase you.

(if I knew how to code the icons in here i would but I'm still new to builds)
Clarity is mainly used for being able to throw out as many little minions as you want and teleport is so you can stay big boss and not let anyone screw with your turrets.

Pretty obvious that you should take a side lane. If possible, with a caster that can boost your passive and be helped by your clarity.

If anyone calls mia or you see that a mid is mia then throw a minion into the river bush for that free ward.