I had this same exact issue the other day, and yesterday, a chunk of my first floor up and disappeared. I used the floor material region, but it doesn't create a "real floor" as in when I place cabinets, they sink below the region. THIS IS DEFINITELY A BUG IN THE PROGRAM. IT NEEDS TO BE FIXED. Waiting on Chief Architect to answer my submission. At this point, I have been using the program for a week and I am less than impressed. So many bugs, quirks, and lack of ability to create what needs to be created. I'm about to tell my boss to return the software and get his money back and buy a better product.