Some sources of turban patterns for cancer patients include such websites as Sewing.org, Headhuggers.org and Guideposts.org. Other sources include In the Loop Knitting and Nancy's Notions.
Sewing.org has instructions for a simple to sew turban that uses a little more than 5/8 yard of fabric. There are only three pieces to cut, and it is easy for charity groups to mass produce. Headhuggers.org features directions for a turban that is crocheted with worsted weight yarn. There is a video tutorial for this pattern, and the website also includes instructions for several types of close-fitting caps.
A pattern for a simple turban that is made with only two pieces of fabric is posted on the Guideposts.com website. The average sewer can make it in about 30 minutes, and the instructions are available as a PDF.
In the Loop Knitting has a gallery of knitted turban patterns that are either free or available for purchase. They come in a wide variety of styles and knitting levels. Nancy's Notions sells a pattern that can be adapted to six different close-fitting head coverings, including a turban. The pattern offers tips for fabric selection and how chemotherapy patients can wear the hats. The turban can fasten with either a tie or a tab.