My hunny bought me a piece of plexiglass at the Auto parts store and used a utility knife to cut it into templates for me. I now have any size I can think of. To get my measurements I have used clear packing tape and taped on an inexpensive cloth tape measurer that I purchased at the dollar store. They work nicely, on a few I have added lines with a black permenant marker.
You will need to lightly sand the rough edges with a very light grain sand paper.