The minimum space for a table is the playing area plus the length of a cue (58") plus about 6 inches for the back swing, more for comfort, on each side. This gives the table:
8'
44" x 88"
14'4" x 18' 4
8+'
46" x 92"
14'6" x 18'4"
9'
50" x 100"
14'10" x19' 4
12' (snooker)
70" x 140.5"
16'6" x 22'5"
"Seven foot" tables vary in size. Work down from the 8' dimensions. "8+" is an "oversized" 8-foot table.
If your room does not meet these minimum size requirements, many billiard retailers will suggest that you can still put a table in, and use short cues (52", or 48"). Many people have found they are unhappy having to resort to shorter cues, and should have either gotten a smaller table, or no table at all. Others, of course, take the opposite view -- they are delighted to have any table.
In the end, only you will know whether you are happy with the room dimensions and need for short cues. Before you spend $2000 for a table that will cause you to smash the walls in frustration, try this:
(1) Find an indulgent pool hall when it's not busy.
(2) Measure your space (at home) carefully, including the distance from the table to all walls that require a special cue
(3) Go to the pool hall with a piece or pieces of plywood or some such, and a short cue, and set up the "walls" to replicate where the walls would be in your house. Play for several hours, using the short cue when needed.
Between two tables you can do with about the length of a cue, the limit is caused not by the cue, but by the player being able to go into his stance between the tables. Deluxe rooms really need more room on all sides to let possible passers-by move without bumping into the players.