http://www.modabakeshop.com/2011/11/...y-playmat.html
here's a baby quilt done that way. i did one with cotton fabrics and batting. but i put my batting the full circle size and that made it a tiny bit difficult to fold over the edges and sew well.
denim can be heavy, if you aren't to sleep under it all will be fine. sew circles into rows and then into rows. good luck.