I've run into this problem before and never found the solution. I have an architectural detail that is a bumped out wall which has a raised floor sort of like a window seat. I built it as a room with a raised floor and do not have a foundation under it. . The siding below the bump out is not showing and also there is a hole in the terrain as if there was to be a foundation - see the attached image. I don't see anything in the Room dbx that would suggest a way to solve this and I'm not certain why the siding isn't showing. I just did a quick test on a basic room and had the same terrain problem but not the siding issue. Any help would be greatly appreciated :-)
Bend ACTIVE Plan 11-14.zip