The Sled Kite was originally made from a sheet of A3 copier paper.
Now, let's be more specific:
It was made from a sheet of 80 g/m^2 copier bond measuring 420mm x 297mm.
No problem there for UK and probably most European folks, but I've realised that 'standard' paper sizes elsewhere are probably different. I have not been able to identify what a 'large' US size may be, except that there are 12" x 18" and 14" x 17" art papers available. So if you are in doubt as to what size to use, try this:
To be perfectly honest, the proportions are not critical, and it's so easy and cheap to make this that you could try some variations and see if they fly (please mail me if they do...) The material can be changed too. Heavier paper works ok, so will lighter paper. Plastic bags can be used, but are difficult to decorate! Newspaper makes a reasonable, if fragile, sled.
In the end, try it and see!
* Thanks to Eric Dobbs for his advice on US paper sizes!