How many rooms are there in a usual Gaijin House?

Every House is different, but there are basically 2 different types of Gaijin Houses:

Style 1 "The Gaijin House"

Some Gajin House are actual "houses" therfore may only have 3-4 rooms available for rent. The owner sometimes also resides at the location sometimes not. They are usually old Japanese houses, So your room will be anywhere from 4-10 tatamis. A 6 Tatami room is a normal bedroom in Japan which is a little smaller then an average North American bedroom.

Sytyle 2 "The Mega Gaijin Complex"

Other Gaijin Houses use renovated or new Japanese dormitory housing units. These buildings can host over 100 rooms. Each room is about 3 tatamis or 6'x10' your average prison size room. Each floor will have shared bathrooms, and wash areas, while the first floor will host a common room, kitchen, showers, sometimes a laundry facility and the reception area.

Of course every Gaijin House differs this is just a basic guide.