Figure a minimum of 5' on each side of the playing surface. So for a 9' table (50'x100' playing surface) you need a minimum of 170" x 220" or 14'2" X 18'4". Just round up and call it 15'x19'.
If you use more than a standard 58" cue adjust these up for the longer cue.
I think for a 9 ft table you really need at least 15 x 20 to be comfortable.... When playing a ball frozen to the rail (even in a 20 ft room) the cue nearly hits the wall....