Snooker tables vary in size depending on the manufacturer. A snooker table of at least 5 feet wide and 10 feet long meets the regulations of English billiards rules. The size listed is the outside dimension. The playing surface is smaller to allow for the rails and cushions of the table.
Billiard cues also vary in length but about 57 inches seems to be about the standard. Allowing about 5 feet around the table provides about 9 inches for the stroke or movement of the cue during the shot. If you include the 6-inch width of the rail, it is roughly 66 inches from the outermost location of a ball to the wall.
Ideally, the room should be 10 feet wider than the width of the snooker table and 10 feet longer than the table. For a 12-foot-long snooker table, which commonly has a 6-foot width, this requires a room 22 feet by 16 feet. Even for tables below the standard size, such as the 8-foot by 4-foot table, the room would need to be 18 by 14 feet.
A minimally sized room allows space for a chair in each corner and little else. Enlarging the room could add a seating area, bar or other game apparatus. This could make the room a more general family entertainment room rather than just a snooker or billiard room.