The invention relates to a building roof structure which comprises a mounting rack, mounting boards, reinforcing ribs and a weather-resistant adhesive. The reinforcing ribs are arranged on the mounting rack and are provided with grooves, folded edge portions are arranged on the peripheries of the mounting boards and are clamped in the grooves, and the weather-resistant adhesive is arranged among the folded edge portions. The building roof structure is simple in installation and stable in structure and improves security coefficients. In addition, the poor waterproofness of a reconstructed ancient architecture roof is overcome, namely the load of a roof can be reduced, and a waterproof roll base layer cannot shed in a later period of adhesion so that the waterproof performance of the reconstructed ancient architecture roof is stably improved.