PURPOSE: To enable a room space to be effectively used at maximum by heaping up prefabricated box-type sections cubically on the same floor.

CONSTITUTION: The prefabricated residential sections of a plurality of prefabricated room sections arranged adjacently on the same floor and to be composed of a plurality of panel bodies with room interior spaces to be formed in the internal sections, are formed. Then, a low-story prefabricated section 6 with a ceiling level lower than that ox other room sections on the same floor, which is formed in the shape of a box, is set to be adjacent to the other fabricated room sections. Then, on the upper section of the low-story prefabricated section 6, a ceiling panel 6b is placed, and a prefabricated section 7 between a roof and a tap floor ceiling with the internal section of a space between the roof and the top floor ceiling is heaped up on said panel 6b.