Here's how I made it:
First, I used my (homemade) sleep mask as a template. It would be easy to sketch one if you don't already have a sleep mask, I'd just draw one big enough to comfortably cover the owner's eyes and then some.
And then I put on some DVR'd 30 Rocks and sat down and hand-sewed all around the perimeter, making tiny stitches, and adding extra stitches around the elastic for strength. I think my sister could choose to wear it with either side facing out.