The first and most important step is making the pattern. I began with some research to find the style I was after. Once I had that in mind, I roughed out a pattern using a hard glasses case as a base.

While card stock worked well to create the initial pattern, I did a few iterations of fine tuning as I made this set of cases. Some things I added along the way were a bridge to support the nose of the glasses within the case, which also provides support for the snap so the hardware isn't pushing into the glasses themselves to close the case. More fine tuning came in with the length of the flap and placement of snaps.

Note that this case is relatively small, perfect for reading glasses or flat sunglasses like those pictured. You will need to adjust the pattern to fit wraparound glasses, or really big framed sunglasses. I recommend printing this pattern and making a version out of card stock first to see if your glasses will fit, and leaving the snap on the flap to last to ensure a perfect fit.