Using the auto-create room function, where the walls surround an area and you create a room by double clicking in that area with the room tool...
If I create concentric walls (of any shape) where one wall is completely inside another area,like this:
The auto-room thing fills the entire area rather than just the outer area, when clicking in the outer part, although the 2 areas are separate, like this
I can create a room in the inner part "on top" of the whole area, but then the sizes are wrong, also, stacking the rooms in the same level could possibly lead to problems with the rendering. Even without those issues, it's not an optimal solution.