Between the opposite sides, the distance is measured where the measurements are removed along the length. With strict verticality of the walls, you can cut the panels over the entire area of the ceiling. If the distance along the walls is not the same, then you need to insert two panels, where each of them will be clarified. Do not forget about the openings for lighting. The first panel is attached to the crate with self -tapping screws, then the subsequent ones are inserted into the grooves of the previous. To close the gaps in the joints, a plastic corner is glued along the edges.