Building roof waterproof layer

The invention relates to a building roof waterproof layer and belongs to the technical field of building technologies. The building roof waterproof layer comprises a metal substrate which is provided with a transparent flexible layer. A transparent protection layer is arranged on the transparent flexible layer which integrates the waterproof function and the function of providing cathode protection for the metal substrate. The transparent flexible layer can generate free electrons through light by means of the photoelectric effect. The building roof waterproof layer adopts the metal substrate with a cavity, so that an excellent heat preservation effect is achieved, and accordingly temperature control energy consumption in winter or summer can be reduced, and comfort is improved. The flexible layer adopted by the building roof waterproof layer integrates the waterproof function and the cathode protection function, the corrosion rate of the metal substrate can be greatly delayed, and the safety service life of