I started off at Joann Fabric and picked out some faux leather (aka vinyl, but "faux leather" sounds way fancier). I liked this blue one.
I cut the fabric according to the design instructions, using my carpenter's square to help draw the angles for the end.
Then I cut the slits to tuck the cords in. The directions didn't really specify the size of these slits. I made mine 0.5" tall and various widths. The first one, shown directly below, I made 1.5" wide for my camera cord. I actually started it narrower, tested it with the cord, and decided it needed to be a bit wider. That's really how I did all the slits -- estimated a starting point, checked it with the cord I planned to put there, then widened as needed. The other slits all ended up being 2", and there's 0.5" between them all.
Next I put the snaps on. They were super easy. I did the end one first, then put all the cords in and rolled the holder up to see where the other half of the snap needed to go. Conveniently, it went right in between the two middle slots.
Here's the holder with all the cords in it. From left to right, they're for my Kindle, phone, iPad, and camera. The phone and iPad also have big adapters to go from the USB connector to an outlet plug. Those were too big to fit in this holder, so I might end up making another one that's bigger and can hold those too. However, the adapters are also simple to detach and don't have pieces to get tangled up with things, so just having them loose in a bag isn't that big of a deal either.
And here it is all rolled up. I used it when we went out of town for Christmas, and it was awesome. Not having the frustration of tangled cords made me very happy :-)