This build is an interesting one I know. I've tested it many times and it works well.

In team fights you should open with Twisted Advance, followed by Arcane Slam, and your Ult. It also helps to Ult when killing a turret to ensure its destroyed; not only will this reduce the damage done to you and your team by the enemy champs, but when the turret is destroyed you kill your ult for damage to any enemies that have stayed around.

In team fights the first three things you should do are always the same no matter what. Always target the squishies first and focus them. Toss some saplings to eliminate runners and to watch for ganks from MIA enemies.

This build is expensive I know from experience; but Maokai is a great farmer. Toss saplings into the middle of minions and boom free money. I only use auto attacks and saplings to farm because if someone on the team forgets to MIA you will need your other abilities off CD to either get away or save your squishier lane partner.

Maokai is an amazing duo lane champ especially with Soraka or another spellcaster like Lux. You have clarity and most likely they will too so you will not have to leave the lane for a very long time, and most likely only when you have enough to outright buy your first item; or you get unlucky and die.

Take care while laning though especially if your squishier partner needs to B, and always toss a sapling into bushes BEFORE face checking them.

Pro:
Saplings deal massive damage. (They're like mortar shells)
Twisted Advance is hard hitting.
Ult is really REALLY useful in team fights now.

Con:
Expensive build.
If you're alone and OOM you're pretty screwed. (But should NEVER happen if you use Clarity)
Farming is not as good as others.