To Design this you'll need:
A 3D design program. I used Autodesk 3Ds Max (because I'm a student :), There are free
alternatives such as Google sketchup for those who aren't students. I don't know how to use that software but megaduty
has posted many sketchup instructables and was nice enough to help me start using the program.
Thats all you need to design it.
Helpful items, A bike, A Ruler.