The recently released batch takes on the subject of map making, speaking about the tech three configuration, custom multiplayer campaigns and a few more aspects concerning custom map making tools. It seems that StarCraft II is going to be a great place for all the mapmakers to create their own unique battlegrounds. The game's producers promise to provide all the needed tools so the community is going to be able to put it's own effort into the game.

StarCraft II Q&A Batch 30

Will it be possible to code the game so map makers can make maps where people can stop incoming spell/missile?

This should be possible through customized ability data and/or triggers.

Will we have selectable male/female of every unit?

No, we don't have plans to include male and female versions of each unit.

Will we have the option to give players the option to change weapons in-game?

While we don't have any plans for a specialized interface for this, it would be possible using the highly flexible ability system.

Will you guys link multiplayer maps, so mapmakers can make multiplayer campaigns?

Yes, we do plan to support multiplayer campaigns and linked maps.

StarCraft II Q&A - Batch 30: Map Maker Series