I made a couple of these ones which I take shopping all the time. I used some orphan blocks for one side and an assortment of fabrics for the other (I love that it's reversible) I think I started with block that were about 6 1/2" and it made a good sized bag with a nice flat bottom. I made the straps a bit longer and next time I will make then a bit wider and put some batting in them to make them more comfortable on my shoulder.
http://www.popularpatchwork.com/site...%20sixteen.pdf