I have a laptop case but I wanted just a little sleeve to keep it protected when I have it around the house.
I had an old sample square of upholstery fabric that I used. First I sewed another scrap of fabric down the center for decoration. Then, I folded in half and stitched up the two sides, leaving one side open.
Since it was a sample piece it was already hemmed. I usually just leave it or tuck it in but you can always sew velcro on.