I got this idea from Gizmodo where someone made an awesome laptop case that looked like an Etch A Sketch - only in felt! So I made this mini one for my DS Lite.
Pattern for DS Lite:
2 x Red Felt in rectangle 2.5cmx8cm
2 x Red Felt in rectangle 2.5cmx14cm
3 x Red Felt in rectangle 8cmx14cm (cut a hole out of one of the rectangles - mine was 10.7cmx4.7cm)
1 x Grey Felt in rectangle 5.5cmx11.5cm

I mainly used these measurements so the buttons I found would look right in the corners.

Sew it into a little envelope (see the second picture) and sew on the snaps, buttons, DS a Sketch in gold thread and then use the black thread to etch a little sketch on the grey felt. Voila!