Geoff, I've made one and only recently. Good on you for wanting to give it a lash. Now there are no doubt plenty of other more experienced leather workers on this fine site but they appear to be less then forecoming, humble poppets they are. so here's the link to the thread that I have documented the process.
http://www.xmarksthescot.com/forum/s...ad.php?t=17283
As for a pattern you can just design one up to your exact specs I suggest. Symmetrical is about the only real guidelines I'd say. I drew it up, went over it in charcoal and pressed it against the leather. You can get symmetry similarly by charcoaling one half of your design and folding the paper to leave the reflection of it on the other side. Ta Daaa! perfect.
Feel free to ask me via post or PM about anything.I'll help if I can.
Erin.