Just want to throw this in -
I've purchased two needle cases. The first one I returned for various reasons, but one of the things I didn't like was it had a tie on it that tended to get caught on things in my knitting bag.
I bought another one a few months ago and I love it!
It has a piece of fabric on the outside that folds over and snaps. Genius! It's big enough to hold all my circular needles and it folds up small. So if you're making your own consider a snap closure.
BTW... NO VELCRO! It sticks to yarn in your bag. Ugh.