I used to cut them out by hand, but now have corner stamps. In attachment some rounded stamps from Amazon and a corner stamp from Zelikovitz Leather's out of Toronto. The Actual corner stamp is >90 degrees and works very well.
Here is a pattern for a Rossi Ranch Hand Boot Holster.
The PDF should be opened in Acrobat and printed as a "poster".
Here are some examples of what it makes:
rossi-ranch-hand-v2.pdf
If you go with snaps, use much thinner leather. There is a lot of pressure on this thicker 8-9 oz leather that would pull the snaps apart. Snaps are popular for travel as well since it lays flat in your suitcase
I'm using Slotted Posts from chicagiscrews.com on the back. Flat head hex screws can be found at many hardware suppliers. I think in the us acklandsgrainger.com is popular.