I'm going to summarize the answers given so far.
The more important point: in English, We don't usually pluralize the noun in compound adjectives. So
Less important, in most English-speaking countries, housing units are characterized by the number of bedrooms they have: it's a three-bedroom apartment, a four-bedroom house. How many people you put in each bedroom is up to you.
Auditoriums and vehicles of land and air are characterized by the number of seats they have -- a two-seat sports-car, a 100-seat jet, a thousand-seat theater -- even though you can only put one person in a seat.
Only tasks, small watercraft, and for some reason tents are characterized by the number of people they hold: a one-person job, a three-man canoe, a two-person pup-tent.