My mother-in-law actually picked up this free project handout for a crayon roll at a fabric store and I thought it looked fairly doable. All it is is a padded piece of fabric with slots on one side for crayon; simply tuck in the crayons, roll the thing up like a sleeping bag, and secure it with the ribbons in the end. My little guy needed something exactly like this since the cardboard box that his crayons came in deteriorated from overuse. I made this a little over a month ago, before I got my new sewing area (yay!), late one night. It took me a few hours because I had to redo a part (gotta love seam-rippers!), but it shouldn't take you too long. Give yourself a couple hours.
I love this crayon roll because it's so convenient (I just pop into my bag before we go anywhere - church, the store, any waiting room, the car, it's always with us) and it keeps everything together nicely. I might add, this doesn't have to be a kid-themed thing. You could alter this to hold your own art supplies (like colored pencils, pastels, etc.) if you're one of those lucky people who can actually draw well. Sigh...I wish I were.