KiwiQuilter, I did the Moose Quilts Jelly Roll sampler quilt along a while back and it was great fun. I don't have a photo on the computer any more but you can see it at
http://wp.me/pJTTP-bd.
Must put a disclaimer on that - I cut my own strips as I couldn't find a good quality jelly roll locally at a price I wanted to pay. And also, if I didn't like a block in the quilt along I swapped it out for something else and used fabric from my stash.
A twin is realistic from one jelly roll if you add borders etc using yardage. Depends on the pattern a bit.
The only other suggestion is to get the Jelly Roll Quilts book by Pam & Nicky Lintott. I have no regrets about buying that one. It's sensibly written and has some lovely designs.
Good luck!