My brother-in-law asked me to make a sleeve for his MacBook a couple of weeks ago.
It wasn't meant to be a carrying bag, so it's strapless. It was meant to cushion the laptop so it can dropped safely into a briefcase.
I initially considered neoprene, because I want to make everything out of neoprene, but finally decided on something more robust and less sporty.
I used fur-back felt for the lining, some headliner (stuff used for the ceiling of cars) for padding, and upholstery-grade vinyl for the outside. The vinyl is thin and soft like leather, and lovely to work with.
The sleeve was so easy to make. The only slightly fiddly part was edging the opening. I'd wanted top-stitching, but my machine wouldn't give me what I wanted through all those layers. So I did it by hand. In order to get evenly-spaced stitches, I perforated the edges of the edging strip with a threadless needle on the sewing machine. Then I did running stitches from both sides
so that the backside looked as neat as the front.