Finally got a chance to write this up. Here are my rough instructions on how to make your own:
1. Cut out the pieces.
2. Sew bias tape to the top of the side pocket.
3. Sew pocket flap top edge (wrong sides facing).
4. Flip pocket flap so right sides are facing and sew the bias tape around the pocket flap.
5. Sew the inside lining.
6. Sew the side pocket onto the side panel of the bag, then stitch on the pocket flap.
7. Sew the outside pieces together.
8. Sew the bag strap.
9. Sew the bag strap onto the bag on one side, and the ring and loop to the opposite side.
10. Sew the front edge and 2 sides of the lining into the bag, leaving the back side open.
11. Turn the bag inside out.
12. Sew the large bag flap into the open back side.
13. Sew the velcro on.
14. Sew any other hardware or adjusters on.