You can use 2 short pieces for a trial run. Lay one piece up on one side and mark lightly along the top of it, lay up the other piece and mark along the top of it. X marks the spot for the top cut on each one. Now for the bottom of the cut; Lay up one piece against the ceiling and the other up against it as if you were going to nail it, make a tick mark on the outer edge of the upper piece, repeat that with the pieces reversed. Now connect the top mark to the bottom mark and make your cut. If the short pieces work, the regular pieces should be a whiz.