Work in progress for Ludum Dare 20.
Move with the arrow keys. Switch items with A/Z.
Use items/paste tiles with X. Copy tiles with S.
(Currently you can also paste with the mouse.)
If the padlock in the corner is green, you can edit the current room.
Click the "just me/everybody" button to decide whether any NEW rooms you create will be publicly editable.
(Leave it on "everybody" if you're not sure.)