I make mine out of template plastic. I just use a ruler and draw a line then disect the center with a line making a plus sign. Then just keep disecting it with lines til you have the sections you want. Cut out the section and add a seam allowance on each side. I use a DVD or a plastic lid to get a curve for the top and then trace it out on cardboard or template plastic. I can cut one or two for you and send them to you. Template plastic is thin not thick.