Using a jigsaw, cut the parts of the box, top and legs to length according to the measurements on the cut list. On the long 1x5 sides of the box, mark the edge 2 inches from one end and 10 inches from the other end.
Using a jigsaw guided by a straightedge, cut off the corners of the 1x5 at each of these marks. The longer cut will be the front of the ramp where it will sit on the floor. The shorter cut will be at the back, or top, of the ramp where it meets the edge of the bed.