I found some pictures on the web and once I found the overall dimensions of R2D2, I was able to calculate the size of each piece. R2D2 is about 43 inches tall and the body is about 18 inches in diameter (not counting the legs)
Google image search is great!
Here's a site that I found very useful: (especially the Autocad .DXF files)
I acquired a few refrigerator boxes at a local retailer and got to work.
I created a frame for the body, then wrapped the cardboard around the frame.
This is a bit tricky. You'll need to soften - but not drench - the cardboard by spraying it with water and letting the moisture soak through the layers. When it's sufficiently soft, you're ready to wrap it around the frame. Apply hot glue to the edges of the frame and attach the softened cardboard sheet to it. I recommend that you get some assistance with this step.
It has a few inconsistencies, but we'll compensate for that later.