I wrapped a sunglasses with paper and made this pattern so cannot explain how to draw this.
I think you can copy this using grids as guide lines.
First, trace the pattern on the 4-5oz. saddle leather and cut it out.
Then, place the saddle one and trace on the back side of the upper leather.
Glue them togather.
And cut the upper leather with seams about 1.5cm.
Glue the seams like this.
For the best result, glue them on the edge at first, then on the back side.
Using this tool is effective for fitting the upper leater evenly on the back side.
Next, using this tool to make holes. I don't think you have this one though, Kaoru has one anyway.
Set kangaroo lace on the needle like this.
Stick the end of the lace like this.
This part would be a lid of the case.
Then, do the same at the bottom of the case.
Lace them up folding like this.
Inside would be like this.
Done! and fit perfectly :p
Then, put a magnet on the lid.
Press the lid on the bottom tightly.
You can get a mark :D
Put the other part on the bottom.
Stick a small patch on the back side of the magnet to avoid scratching.
Put a button that I made on the back side of the other magnet for covering.
If you have any questions, feel free to ask me ;-)