So I made a custom sleeve for my MacBook Pro out of a felted woolen blanket and a tent canvas. Both materials I bought in a swiss military shop during my last trip to my home country.
Step 1: What you need
of course the usual sewing supplies...
some ruler (take the long one)
as well you will need a drill with a 4mm drilling bit
and lots of patience
Step 2: The inner sleeve
I spreaded out the blanket on the floor, put my laptop on it and tipped it over three times so I got the right amount of fabric (four times the surface of the laptop plus some extra for sewing)
I sewed together half of the sides, then folded back, fixed the edges and sewed together the bottom edges (see images)
Step 3: Outer sleeve, part one
The buttons on the canvas are doublesided, so I needed to drill them out, because otherwise they would dent or scratch the laptop...
But don't throw the buttons away, you will need them later!