Jelly roll pans usually come in two different sizes. You can get a 10 1/2 x 15 1/2 x1 or that is equal to ten cups. The other size is 12 1/2 x 17 1/2 x 1 or that is equal to 12 cups.
Most jelly rolls are just rolled out on a standard cookie sheet, which is about 9 by 13. An actual "jelly roll" pan measures about sixteen by eleven. Most people use cookie sheets.
Generally, a jelly roll pan measures 12" by 15" with 1" high sides. They are available in other sizes though, so it's possible to get a smaller or larger one.
