Well, instructions for making these have been posted many times, but basically, the procedure is to use fabric covering (not monokote) and cut into strips about 1 inch wide. (you may alter the width per your needs)

take two strips of equal length and place them back to back with the sticky side out. Then run through a sewing maching to sew the two together lengh wise down the middle.

Then you simply fold along the stich line and iron them on. What you end up with is two pieces of fabric covering with the stitching as the hinge. Then, you can cover as normal which will cover up your hinge material. I use white world tek fabric covering, but other brands would work just fine.

This is the only type of hinge I use any more. They are very simple to make and install. Plus, no hinge gaps.