Getting your hands on one that you like and copying it is certainly the best route if you have decent leather working skills, but working from photos works well too. Check the eBay listings for all the photos you could ever need.

There obviously is no one right way to do it, and with 15 hides you'll want to make several anyway. Make patterns out of paper...I rough out a pattern then make a final copy by tracing around buckets or paint cans to make uniform curves. Gusset material should be soft and at least 2" wide.

And, by the way, welcome to X-Marks.