Thank you very much okh! I missed that option. Maybe because I am working with a different language. Now it works as expected. Now I just need to tweak the roof a bit to get rid of the beams.

I added a roof, but now I do not see the second floor from the first floor when I look up. I do however see the first floor from the second floor when looking down [:-/]

You wrote put the floor on a separate level. What do you mean by that?

Here is my plan for the first floor.
I will look at how to add a roof, but what I quickly saw yesterday is that it is not that easy.

I am trying to create a room with a sloping ceiling. I succeeded in creating the sloping ceiling, but because the room has a sleeping loft I am creating it with 2 floors. I created the first floor with a room for the sloping ceiling, one for the loft and one for the room itself for the flooring ...