To enable installation of dwelling units of a desired size on stepped sections of a rooftop within the scope of regulations applied to collective housing.

Dwelling units A1, A2, ... and B1, B2, ...E6 are arranged in a staircase pattern, and maisonette-type dwelling units 3, each comprising lower and upper stories 31 and 32 which do not vertically overlap with each other, are installed on stepped rooftop sections. The upper and lower stories are in communication with each other via a staircase 4 provided astride a step section 2, so as to secure a desired area. The front sides of the lower and upper stories 31 and 32 of the maisonette-type dwelling units 3 are recessed from the sides where regulations are applied, so as to narrow frontages of the dwelling units; hence, relatively large roof balconies 61 and 62 are formed before the lower and upper stories 31 and 32.