Been looking for a simple design to make a sheath for my favorite scissors recently.
Ended up with the following 2-piece design:
Used a 5 oz veg tan for it. It turned out to be really simple to make, even with my very limited skills and experience...
You'll just have to add some kind of a belt loop on the back – mine was done to hang on a wall.
No wet forming was used, the leather turned out to be flexible enough to follow the shape.
Hand stitched.
And yes, I store the scissors in it all the time, but it is a pretty dry environment. Otherwise I would soak the inside of the sheath with some oil...
Good Luck!