This is just a random build i made on my first game with Maokai and it worked pretty well. Items will change depending on your team and the situation.

Max sapling toss as soon as possible then get 1 in twisted advance first then arcane smash 2nd. Once you got 1 in each max twisted advance 1st. Whenever possible put points in vengeful maelstrom, if you've maxed "E" already.

I just use Heal and Teleport because it helps me stay in longer and get places faster. Whatever you pick here is up to you.

Pros:
-Great HP
-Great harass
-Great support
-Ultimate is very helpful and useful
-Just play to see how amazing he is. (May take practice) lol

Cons:
-No way to escape ganks unless you pushed past the enemy minions and use "W" skill to go back.
-Can 1v1 but have to be careful and smart.
-May be targeted first in ganks or team battles.

You can use sapling toss to farm but i suggest you save all the mana you can until your at a comfortable mana lvl. You need all you can to harass and fight the enemy champions.

I don't really use the rune setup i put on here I use HP/CDR runes. I know i should give a good rune set on here but i say put w.e you want with this character. :]