Abstract: A facility cover in the form of an extensible shed has movable arches that support a flexible canvas cover. The arches are modular and are connected in groups by diagonal elements hinged so as to form parallelograms with pantograph movement. The ends of the shed have at least one arch of reduced height so as to form an apse shape. Folding elements are provided on the sides of the shed that cooperate with the hinged parallelogram structure so as to assure that the cover folds outwardly in a bellows fashion as the arches are moved close to each other. As a result, the folding of the cover does not interfer with the movement of the arches.