I would like it if you could assign a fill pattern and background colour to a roof or slab just like you can to a wall. For example you could apply a tile pattern to a slab rather than having to use the fill tool. Moving the slab the fill would go with it. You would need a handle to orientate the fill.
Also if you have slabs that overlap each other on the same story you could use the bring to front and hide the lower slab with the upper slabs background fill.