The best method to getting an area that you need to change and get the new area easily, is to use the macro Blocker. The area (and overall dims, room name, etc.) can all be shown on the drawing if you need to, or just be visible and not print. Once you put the boundary in with Blocker, and you change the boundary, you just need to reopen Blocker and the area is updated.
This is how I think Smart Floors will need to work in v17.