The present invention relates to a prefabricated greenhouse for a building rooftop which can be conveniently and easily assembled at a flat place of the building rooftop to allow the cultivation of various types of vegetables. The present invention includes: a base bracket main body where lower brackets are disposed on both respective sides of a connection member and vertical brackets directed vertically upwards are disposed at the respective lower brackets left and right lower frames which are coupled to the respective lower brackets and are arranged in parallel to a rooftop bottom surface left and right upper frames which are coupled to be directed upwards to the respective vertical brackets and form side surfaces and a roof of the greenhouse a central bracket main body where side surface brackets coupled to and supported by the upper frames are disposed on both sides of the central connection member, so upper portions of the left and right upper frames are supported a roof finishing bracket main body where a horizontal bracket coupled to a ridge frame is disposed in an upper portion of the connection member which is positioned to be directed vertically upwards to be coupled to and fixed to upper ends of the both side upper frames, upper inclined brackets are disposed on both sides of the horizontal bracket with a downward inclination, and downward inclination brackets are disposed on both sides of a lower portion of the connection member with a downward inclination a greenhouse front-back frame which is disposed in transverse/lateral directions to form front-back surfaces of the greenhouse a door which is disposed on one or both of the front-back surfaces of the greenhouse, so people can come in and out and a fixing means for safely and firmly fixing a transparent film covering the roof and four side surfaces of the greenhouse.본 발명은 건축물 옥상의 평탄한 곳에 간편하고 용이하게 조립 설치하여 각종 채소를 재배할 수 있도록 한 건축물 옥상용 조립식 온실에 관한 것으로, 그 구성은, 연결부재의 양측에 각각의 하부브래킷이 설치되고, 그 각 하부브래킷에 수직 상향하는 수직브
