I used this tutorial as my starting point, but couldn't resist doing my own thing. First of all I quilted them instead of adding interfacing. My handle is shorter and narrower than in the original and I added binding strips to the seams on the inside, handstitching them closed to make a nice finish and make sure yarn or needles don't get tangled up in fraying raw edges.
Once I had finished the first two, and deciding that they were a bit smaller than I wanted, I had a bit of a rethink, and came up with the solution of adding square end pieces. It was a bit fiddly to sew, but I manged, and I ended up with bags that are just the right size for a couple of balls af yarn and a half finished shawl.