In my son's middle school, they have restrictions on the size of the bag they can carry around. Last school year I made my own pattern thinking it would be easy but it ended up very involved. I used the one I bought from the school, at the beginning of the year for $15 that was coming apart at the seams as a guide. It was made from cheap nylon and no lining. My remake had a cotton print outside and a ripstop nylon lining inside with grommets in the corners like the original. I used some thick cording for the straps/drawstring and it worked. It took me all day to figure out and 3 hours to make but it held up the rest of the year and his friends wanted to buy it off him at the end of the year.
It was successful but this past summer I saw this pattern at a Jo Ann's and decided to buy it.
It comes in mini to medium and the biggest size was within my 17" X 15" maximum limit.