The ones I've made have been from heavier fabrics (denim or home decor fabric) and not quilted, but they could very easily be adapted to your purpose.
I'll try to get a tutorial done for you, but it may be a few days. The actual bag can be easily done in an evening, but getting the instructions stated clearly may take me awhile, since I don't actually have a pattern per se, just figure out how big I want it and sew it up.