To improve the efficiency of transport or the like by placing roof panels of a second roof unit in an inverted manner on the roof panels of a first roof unit and producing a second roof unit by attaching a roof truss portion to a roof panel.

A right angled triangle-shaped support panel 111 is arranged on a support base K, a rectangular support panel 112 is connected and a roof truss portion 11 is formed. And the roof truss portion 11 is connected to the roof panel 12, and a roof unit 1 is produced. Then, the roof panel 42 is placed by inversion on the roof panel 12 of the roof unit 1 and both of then are fastened and fixed by a vice 7. In addition, a right angled triangle is assembled in an inverted state to the roof panel 42, a rectangular support panel 412 is coupled and a roof unit 4 is produced. Also, when transporting the units 1, 4, a unit 1 with the eaves side facing upward and a unit 4 with the ridge side facing upward are matched to roof surface of the roof panels 12, 42 and loaded to a truck thereby making the transportation efficiently.