This type of roofing consists of main load-bearing beams, in the shape of half casks or drums, and flat covering panels between the main beams and between these and the perimeter of the tank to be covered.

Due to the superelevation of the central part of the main load-bearing beams in comparison to the ends, resting on the perimeter, there is a
uniform slope that serves as a runoff for
the surface of the cover.