My friend came up this weekend and we spent practically the whole weekend planning and making yoga mat bags for her and another friend. You can see the bags here and the machine embroideries that we did on the bottom of the bags. I think that the embroideries add a really special touch. You can also see the little sun logo that I put on the bags incase I decide to make more. I really love them both and didn't want to give them up when they were finished. The rest of the weekend we spent planning and having a birthday party for my two boys. :)
Basically the bag is a tube with a round bottom on it and a drawstring top. Measure the width of the mat to get the length of the bag and roll up the bag ( I did it loosely) to get the diameter. There is a great free computer program at http://www.wildginger.com/wildthings/ that is a free bag making program. You just type in your needed dimensions and it will give you a pattern. There is also a great pattern book that includes a zippered yoga mat bag by Cindy Taylor Oates called "Purses, Bags and Totes" http://www.sewthankful.com/PursesBagsTotesPatternBook.html I have not made this bag yet but all her bags are great and I want to get this book.
If you want more information on the bags please post a comment here and I will blog on the directions more.