To improve work efficiency of roof construction by erecting upward the bottom of a recessed part which is expanded toward the back and circular in plane in the central part of the surface of the top of a tight frame, and integrally forming a cylindrical screw-in guide part with the upper end part projected from the surface.

A cylindrical screw-in guide part 21 in which a tightening screw for supporting and fixing a roof plate is screwed is formed on the top 17 of a tight frame 15. The screw-in guide part 21 is formed integral and cylindrical so that in the central part of the top 17 of the tight frame 15, the bottom of a recessed part 23 circular in plan formed on the surface of the top 17 is folded back upward and erected to project the upper end part from the surface. Thus, the roof construction work can be simplified, and firm fastening of a screwed part can be achieved without easily damaging the screw-in guide part 21 so as to secure safety in construction work. Further, an accurate and clear mark can be put on the upper bottom of the roof plate so as to construct a roof with beautiful appearance.