In my opinion maokai is one of the best ap heroes in the game. Every1 thinks it is so awesome to use him as a tank for his ulti giving u +20% decreased damage from almost any attack. Well here I'm going to present an ap build with which u should survive most even team fights

What about runes. I chose the most ap type runes. Why? It gives additional ap. In my opinion it is uch better for him to use his sappling toss away from enemies and decrease their attack slowly. then jump on them with twisted advance and crash with arcane smash, exhaust and ignite. I think that so huge defense isn't needed for this hero.

Masteries are chosen thinking about his ability power. Not his Cooldown reduction. In my opinion CD is low enough for most users. dodge is taken for saving his life in early game when minions together with enemies focus on him.

items should be picked depending on enemies. WHen they have more ad abyssal scepter isn;t needed and should pick thornmail instead. And ofc when there are more ap heroes u don't need zhonya and u should pick force of nature. I know this will lower ur ap but u will die much slower.
Why rylai's scepter and rod of ages? Because they give u lots of ap, health, some mana which will be needed for ur spells and at last it slows enemies. Health is also important for ur passive which heals 7% of ur max health.

In my opinion this is the only good skill sequence there is for every game. In early game u toss ur little bug and deal huge damage to enemies. When some1 with low hp goes away u pursue him with ur twisted advance ignite exhaust and gg.

Good luck :) hope will be helpful