I don't use much of a pattern when the knife group is all shapes.
I lay the knife on the leather and mark off around the knife then cut it out.
I then case the leather and push it in around the knife. At this time it takes a little shape and you can start marking trim lines . I like to leave a good 1/2" on the stitch line and I leave it that way till it is stitch then I trim it. That will give a nice smooth welt with little sanding..
Make sure your belt loop is placed so it won't be in the way when you stitch up your welt.
It can be great fun making knife sheaths and I think it is my most enjoyable work in the saddle shop. I have turned into a knife junky
