Plate roofing material

A plate roofing material having a length which is parallel with a slope of a roof and a width which is perpendicular to the slope, the plate roofing material comprising an irregular upper surface including an exposure portion (2) and an overlap portion (9) along a length thereof, said exposure portion (2) being exposed when installed on the roof and said overlap portion being overlapped by an exposure portion of another plate roofing material when installed on the roof, said plate roofing material having a somewhat uniform smooth back surface over its length and width, said upper surface overlap portion having a generally flat surface, said upper surface exposure portion (2) including at least one longitudinal groove (7) extending from a lower edge of said roofing material on said upper surface exposure portion across a width of the roofing material up to said overlap portion, said at least one longitudinal groove being approximately V-shaped in cross section along the width of plate roofing material, said V-shaped cross section having a narrow part and a wide part with the wide part at the lower edge of said plate roofing material extending in a direction toward the narrow part and to the overlap portion, said longitudinal groove having a plurality of irregular stepped side surfaces and a linear bottom groove having an approximately constant depth and extending from said lower edge of said plate roofing material to said overlap portion.