PURPOSE: To improve workability while positively preventing the intrusion of rainwater by stacking ridge flat tiles on both sides of a ridge edge only by the fixed number of stages and filling space sections formed among the ridge flat tiles with a foaming agent.

CONSTITUTION: When roof tiles are arranged to the top section 2 of a roof under a specified state and a ridge is shaped, ridge flat tiles 8, 8 are stacked on both sides of a ridge edge only by the predetermined number of stages respectively at first. The space sections of the ridge shaped among ridge flat tiles 8, 8 on both sides are filled with a foaming agent 11 under the state, and the ridge flat tiles 8, 8 are fixed. Channel tiles 13 are arranged at an uppermost stage, thus finishing the ridge. Accordingly, the foaming agent 11 is spread to not only the space sections of the ridge but also the corners of each ridge flat tile 8, 8, thus positively fastening the ridge flat tiles 8, 8 without using ridge covering soil such as kneaded soil.