Cassandra...........when I did the bag, I just made one of the blocks that I used in the blanket and went from there. I quilted as I went. Then I did the sides because I wanted to make the pockets. Then I measured for the bottom of the bag. I also did the inside pockets before I put it all together. What I did for the straps was take the heavy black straps usually used on backpacks and covered it with matching fabric. That way I knew it would be heavy enough. I just made a flap for the top and stitched it on. I used heavy duty snaps to do mine, but velcro would also work just as good.
I have tons of patterns for bags, but none that I liked as a diaper bag (or whatever else it could be used for). So I just made my own.
Barb