We have only used wide binding twice. The first was store bought and already folded and pressed, so we had a pattern to make our own the next time. You might check at Joann or Wal-Mart or HL and see if you can buy one to use as your example.
I think when we made the binding it started at 3" and finished at almost 1". We folded it WST so that about 1/8" of the bottom was visible and pressed. Then we opened it up and folded both raw edges almost to the center and pressed them. When we put it on the quilt, we put the "shorter" side on first and sewed on the fold, mitered as normal, then stitched down the other side. We love the look of the wide binding. I don't know why we never think to try it again.