Knife sheaths are made with a welt around the entire blade then hand stitched to the back and front piece of leather. No rivets are used because they are not needed with the hand stitching. I don't typically make the folded over leather sheaths that are common simply because they are designed to be quickly machine made.
I can also overlay your Kydex sheath, if you want something that looks a bit nicer than black plastic surrounding your knife.
Most often I will need your knife, or at the least, several pictures that include the knife next to a ruler and the thickness of the blade. It is much preferable to have the knife in hand when making a sheath.
Thumb-Break Style Knife Sheath
Knives that have holes in the handles can have sheaths made with a thumb-break style retention. This is where the back of the sheath comes up just past the first hole in the handle, and a copper rod is placed so that it fits into the hole. You push the top of the sheath away to release the knife.