I am able to recreate the process to show how to make a leather eyeglass case that is similar to mine. Unfortunately I am not able to show the stitching and fastener installation, but there are plenty of online guides that will show you how to do it.
Step 1: Getting Started
Smooth out the case cover and trace it onto a piece of paper, as seen in Photo 4. I traced mine onto a thin piece of cardboard to make a stronger pattern. A pattern is useful if one needs to make alterations to ensure the best fit. It is also useful if one desires to make additional cases later on. Cut out the pattern and then trace onto a piece of leather. The leather should be about 1/16th of an inch (2-3 mm) in thickness for a good strong case.
Alternatively, skip the pattern making and place the case cover directly onto a piece of leather and trace the outline onto the leather as seen in Photo 5.
Use a sharp pair of scissors to cut out the leather.
Step 2: Sewing the Case Together
TIP: Start sewing from the middle part of the case and sew your way down to the bottom of the case. Looking at Photo 2, that would translate to starting from the right and sewing in a direction to the left until you reach the bottom. This keeps the final knots at the very bottom of the case where they can be tucked away out of sight.
Be sure to finish your stitching so that the final knots are inside the case as seen in Photo 2.
Your finished seam should look something like my stitching in Photo 3.
Step 3: Adding the Fastener
If the fit is too tight, moisten the leather from the inside with a damp sponge or paper towel and fit the plastic protector in place. Leave the plastic protector in place and let it dry overnight.
Adding the fastener is the last step. Be sure to purchase a quality solid brass or stainless steel fastner. This type of fastener is also known as a "Sam Browne Button".
Make a mark on the leather at the location where you want the fastener to be. Remove the plastic protector and punch a hole through the leather. A leather punch works the best to make the hole but an awl or nail would work as well.
Insert the back part of the fastener through the hole in the leather (Photo 3) and mount the front round piece on top of the back piece and hammer the two pieces together using a setting tool available in leathercraft stores (Photo 4).
Fold the upper flap over the fastener and mark the location on where to punch the final hole. Adjust the hole size so that it fits snugly over the fastener as seen in Photos 5 and 6.
Step 4: Finishing Touches
As I noted earlier, I have had my leather eyeglass case for about 10 years now and it still performs wonderfully and has aged beautifully. Your new case should do the same for you and last a lifetime!