I knit a cozy for my nano, I didn't use a pattern. Just made it up as I went.
I used bulky silk yarn, cast on 7 st (about the width of a nano, adjust depending on yarn/gauge) on #7 needles and knit garter stitch until it was long enough to fold over itself and fit the nano inside. Then cast off, fold it onto itself, stitch up the sides and turn it right side out. It ends up being the same shape as the little pleather case it comes with, only thicker and more protective.
But, honestly don't waste your time, this thing...
is way better than anything knittable and it's not to expensive. I have one and it is GREAT. it's only a hair larger than the nano itself, it's practically indestructible and provides serious protection without blocking any of the controls.