For nine standard (large fowl) chickens the going recommendation for inside the coop (house) is roughly a minimum of 4 square feet per bird. For the "run" (fenced in outside area) the recommendation is usually at least 10 square feet per standard chicken. Thus, the minimum recommended square footage inside the coop would come out around 36 square feet and the minimum area inside the run would come to around 90 square feet.
Anything that takes up floor space (feeders, waterers, roosts, etc.,) also reduces usable floor/run space.
A 4'x8' coop is a standard size and would probably hold your birds ok. It could be built raised or as a walk in. If you think you might get a few more chickens later then double it to an 8'x8' (or larger) walk-in.
A lot depends on...your area/climate, whether you are urban or rural (any restraints?), the types of chickens, your budget, etc.,.
Hope this helps,
Ed