When I have a gig to add a new level to a client's house they aren't allowed to do this. Apparently, this isn't caused by mods either. Or when I am supposed to add a walk-in closet in an existing room you can't do that either. You have to add a whole new room off the existing structure and you can't add doors or archways connnecting. I have to come back in Managing Worlds and go into build mode and fix up the renovations afterwards to get them the way I want them to look. On a positive note though the clients usually just love whatever you do as long as you follow their likes.