The invention concerns an architectural cover for application to a roof or wall. In particular it concerns a rectangular architectural roof cover (or wall mounted shading device) that includes retractable and moveable louvres, comprising: A near end of the rectangle and a far end of the rectangle. Two spaced apart beams forming the left and right sides of the rectangle. A series of louvres spanning between the two beams. Wherein, the ends of each louvre are connected to a respective carriage. The carriages on one side are mounted to run to and fro along one of the beams, and the carriages on the other side are mounted to run to and fro along the other beam. A mechanism is provided to drive the distal carriage on each side to and fro to extend and retract the louvres.