I thought about how to determine the exact size my doors needed to be for the correct fit.

I measured the opening and deducted 1/4" all the way around the door opening to achieve my door size. I then took the plywood that I cut from the door opening and found it to be 5/16" bigger all around then I needed (based on the KuffelCreek Plans). I built this jig to score 5/16" in from the edge for the plywood cutout. Hope my measurements are correct!
Preparing to cut the Doors to Size