maokai is a tank but has a great spell set. i abuse that in this build.
starting up.
in the begining your goal is to spam saplings to push and damage enemy champions.
mid game.
in mid game when you have your sorcers boots then you can start to charge in there. get close usesing your twisted advance. it will keep them in place while you throw a sapling about 2 feet in front of them. all tell you push to the turret then your ulty will be usful there.
late game.
now its come to this. you should have your rod of ages. now you should be able to do lots of damage and take lots of damage as well. same as middle game but you will most likely get ganked or help gank you you useful for this stage. you can pin enemies down push them back and give turret protection. this the build i use and seems to work for me. i use ignite to do extra damage and get 10 ap while its on cooldown. i used to run out of mana when an enemy was almost dead so thats why i choose to get alot of mana and my second summoner spell. espicial at the begining.