Hello I am BlackLancer and I've been playing Maokai for over 2 years. Since season 1 there have been a slew of item changes and variety, and I think I've found the correct build for Season 3. I have had some great games in Diamond with this build and was requested to share it with everyone.

The runes are your basic AP mid page, replacing MR with Cooldown. The reason for the CDR is because Maokai is so reliant on cooldown mid game, it isn't even for early game. Early game you do not have the mana to sustain sapling spams, but with doran's ring mana return you can afford to throw saplings to farm. The CDR is necessary to farm under tower / in lane. At level 1 you will have 17% CDR, with Athene's it will put you at 37% which is ideal.

Masteries are played similar to a ryze, they give you mobility and cooldown reduction, exp also helps because Maokai outfarms most mids (because he can go through the wall to farm wraiths). A nice blend of 9/0/21 helps you keep damage, but 21 in offense is not necessary because you do not build as much AP as a traditional AP carry mid, more tanky so the utility comes in at a much more useful cost.

Doran's ring is a strong start.
Against other AP's you need some MR and Mana regen always helps so Chalice + Merc Treads gets you decent MR. Add an abyssal later on.

Against AD mids, you need to rush that sunfire, but that allows you to go sorcerer shoes mid, and even ignore the chalice if the whole team is AD, getting more damage with the spectral wraith (spell vamp is awesome too).

There are a large variety of items you can buy. The two most crucial are Sunfire(when you go in, it does free damage and gives you the tankiness you need to play Mao) and Rylai's (you generally get this late game but the slow is great for catching people with saplings).

Merc treads are generally recommended even against AD mids for tenacity if they have CC. Only ignore merc treads if the enemy team only has slows, not stuns. Stuns will ruin your combo.

This unique skill sequence order is made for farming, and all in'ing past 6. With the added damage from Q and E level ups, you can all in someone without using your ult because your ult simply uses too much mana. Once you have enough mana sustained from leveling up and consistent blue buffs / items, then you can start to use your ult in the burst combo. It is simply overkill for most champions and not worth the mana. Try and just snare and full combo at levels 8,9 and you will be surprised how much damage you can deal with only ~50 AP.

Not much to say here. You can run teleport if you face something like a TF mid. I would never advise going barrier, possibly run exhaust against melee AD mids (rengar, riven, etc).

After level 5 you can 1 shot the back wave with saplings.

A neat trick is throwing the sapling on the back wave, hitting the front wave with Q knockup, and the back wave with Q stream, then the sapling comes back to kill the front wave. Note this does not work with cannon minions. Late game just use sunfire and Q to farm, no use to waste saplings unless distance farming/wave clearing.

Whenever you push and you have blue buff, send a sapling in the center of wraith camp, then W to the closest wraith. Easy wraith camps will have you outfarming Froggen in no time.