I cut two fabric rectangles, about 20" wide by 18". I put right side together, sewed 1/4" around all the edges except leaving about a 4" opening. I clipped corners, turned right side out and pressed flat. At this point it's about 19 1/2" by 17 1/2".
This is the pathetic one I made a few years back, woefully inadequate. But I learned from it: make it wider, for more needles (10 sizes)! Make two rows, for double pointeds and regular needles! Leave wider space for each size! And make it nicer looking!