First I made a large letter in Word on a paper size template and drew a line as a guide for the height of the letter. I printed off both, the letter on scrap paper and the line guide on nice cardstock.
Then I laid out my crayons and cut them to the right lengths to fit over the letter template. I used an exacto knife to make the cuts. The crayons on the curve must be cut at an angle. Once I had my letter perfect (and in a ROYGBIV color like order) I transferred them one at a time to the cardstock with the line quide (so that I wouldn't have to worry about any of the letter showing through) and glued them with Elmer's glue. I felt more comfortable using Elmer's glue than hot glue so that I had some freedom to shift the crayons around after I set them down. Make sure your cut edges don't have any crumbly edges or else when it is all finished you will have wax crumbs falling to the bottom of the frame, so blow on it to test for any strays.
Then I set the frame on top and cut a piece of thick cardboard to fit the back. I had to make my own backing because the one it came with wouldn't fit right with the crayons. I gave it as a gift to a teacher with a nice stand to display it on.