I did...for the circulars I have. However, I was making it up as I went, and upon completion, found a problem with it. I am, when I have more than a day off work, going to take it apart and change it. I also got more fabric to make one for the lady who taught me to knit. She and several others want me to make them to sell, but I can't figure out how worth it it would be.
Just sit and think about what you want, then do it!
As an afterthought....I was looking at patterns last week to make a bag for knitting, and Simplicity has a real nice one that includes things for your knitting needles too. I still think I will make that bag, but not the holders they have included on the pattern, which is #4542. You can go to simplicity.com to view it.