Watson, I don't really have a 'pattern'. The body is about 34-36 inches long by about 18 inches wide. The cut out for the base is 3x3 (if using 2 pieces that will be sewn together at the base) or 3x5 1/2 (if using a whole piece). That is as much of a pattern as I have.
I plan on a pieced side of a bag being about 18x12 finished with an anchoring strip at the top and then a bottom piece that includes the base. That is as technical as I can get I think. Kind of piecing 'by the seat of one's pants"?