The easiest and moswt practical one that i have seen is simply two pieces of heavy fabric sewn togetherat the tops and, depending on the size of the needles and how many you have, at half inch or so intervals all the way down. youare making a bunch of tubes into which you will insert the needles. their strings will be in the case adn then they will wrap around and live inside the case which can roll up into a tube. not sure if any of this makes anysense. i wish i could sketch something because it is so simple and practical. if you want to you can also do some fancy little painting of sizes on the fabric if you are not lazy like me and just eyeball everything. : )
Good luck and hopefully I am not nearly incoherent as I think I am.