I like the concept! A couple of comments:

1. When you add a second room, the dimensions of the first room should be copied over as a default.
2. Placing a sprite (and moving on to the next thing) is not very intuitive. Maybe some kind of quick tutorial?

Following this with interest

Thanks for the feedback! 

1) that is a good idea and easy to implement, will add it in the next version :) 

2) I will overhaul the room editor soon, I think, I have some ideas how to make it more intuitive. Hopefully then it won't need a tutorial!