Consider in-game (or out of game editor)

[cnlohr]

We need to have support for some sort of editor. Even for computer scientists, trying to guess everything in code is a pain.

[phiresky]

Probably extending the placement/removal of pickables you already have. Just using that while selecting the block types (minecrafty) would already be a big improvement.
Then maybe area placement.
What might also help is room-relative coordinates.