I measured the longest tool i use my "pokey tool" and added on a few centimetres to the length to get a size to work too.
I crocheted a rectangle the required length and allowed enough width to fold over a flap for the lid and also a flap to make the purse, ie make your purse 3 times the width required for the finished.
I then finished the design by crocheting the edges together and adding a few handmade crocheted flowers. One of the really great things is that unlike a metal container or plastic box the tiems dont rattle around and make a racket when i cart them around in my various craft bags.