For the sheaths for these knives, I used 8 Oz. Tooling leather. It always starts with a cardboard template that I fit to the knife until I am happy with the shape. Leather is not cheap but cardboard is free. Then I transfer the pattern to the leather.
After folding the belt loop and attaching it with two brass rivets, I used a swivel knive to cut in an outline for a pattern I would be tooling into the leather.
Then I wet the leather so the tooling will remain after the leather dries.
I used a pear shaped shader to dimple the leather. Here's what it looks like after it dried.
Next, I wetted the fold line, added a welt and used rubber cement to join the welt to both halves of the fold. The welt protects the stitches from the knife blade. Then I punched the stitching holes.
After stitching, I trim the excess leather for an even outline. Then the sheath is soaked in water and fitted to the knife. Its like working with clay. The leather takes the shape and stays put while I use a hair dryer to dry the leather.