I started by creating a template out of cardboard.
Hand-sewn with hemp string.
A strong magnet closes the cases firmly and allows super-easy opening.
An updated version has a piece of birch veneer glued on top of the magnet to prevent it from slipping through the hole. The stitching is nicer, too.
This picture can help if you want to make a case yourself. One square = 1 cm. You might want to try to make a paper template first.
