New version (1.1) with few improvements.
Now, by check/uncheck the SUBTOTAL, check/uncheck all rooms at that level.
Checking a room on unchecked level will also check the level.
The plug-in are under menu Tools->Total room's surface.
I recommend to remove (uninstall) other plug-ins with the same functionality.
The new version could be downloaded from here:Roos Surfaces v1.1
or from Source Forge here.