The utility model discloses a construction is on - -spot with portable model in kind, including an automobile body that is equipped with the guide rail, be equipped with the backup pad on the automobile body, be equipped with the drive arrangement of drive backup pad rebound between automobile body and backup pad, be equipped with the job site model in the backup pad, the job site model is including locating the parapet in the backup pad, be connected with the roofing structural slab with the parapet bottom, the roofing is stated structural slab top and is equipped with in proper order with the parapet junction and looks for the slope layer, the heat preservation, the screed -coat, waterproof layer and protective layer, it has the blast pipe to look for the slope in situ upwards to extend to the parapet, be equipped with the exhaust hole on the blast pipe, the blast pipe is through the screed -coat, waterproof layer and protective layer be outwardly directed to have the gas vent, it has the protection casing with automobile body guide rail sliding connection still to include, the protection casing bottom is equipped with the lift leg, still be equipped with the curb plate on the automobile body, be equipped with the tractive unit on the curb plate. The utility model discloses simple structure, it is convenient to remove, circulated used repeatedly, economical and practical.