To solve the problem that it takes a long time before to measure the size of a cut tile in a laying site and then cut a flat original tile on the ground or a roof according to a necessary size and operation efficiency is not good, and to solve the problem that many waste materials are produced and disposed of at much cost.

All cut tile shapes of a right downward corner ridge and a left downward corner ridge constituting one flat part roof surface are calculated in a factory etc., according to a roof size in the laying site by measuring the roof size in the laying site or making calculations by a computer in advance so as to solve the problems, cut tiles of the right and left corner ridge parts are suitably combined on the one flat original tile so as to reduce waste materials, and cut tiles of each of right and left corner ridge parts are cut. Cutting shapes are one of a Y-letter shape, a V-letter shape, an inverted chevron shape, a lower-case-letter (y) shape, or an X-letter shape.