Thanks Flatcat and Giorginetto,
I'm building a flying castle. The first floor shouldn't be made of wood. And do not have mucht flooring to begin with (although I now have 4 houses, 2 castles, 1 schuldturm, and 3 loose roundtowers).
I had some free time wednesday, so I did some sawing in the garden. I can now make an improved version this weekend. More pics coming up.