I also made one out of a page from a magazine. When making it out of paper you want to make sure they paper is thick enough, so I glued two sheets of paper together. For magazine pages I used .5 inches by 9.5 inch paper.
The dimensions I stated are the minimum lengths, in proportion to the width. You could go as long as you want and keep the same width. But you cannot go wider and keep the same length. The longer you go the looser the ball will be.
Video tutorial is here: part 1 and part 2.
A reader just updated me that this ball is called Greek Soccer Ball by Kunihiko Kasahara. I was taught how to make this in high school by a friend so I never knew what it was called. Thanks Maria!