Step 2: Make your shark patterns
A major factor in the size of the shark relative to your body is that it has to have a large enough mouth to wrap around you without the body looking too short and stumpy. It will probably have to reach right up to your chest rather than sensibly around your waist - this costume is about fun and effect, not comfort and convenience!
The shark's grey back is made from two identical halves, one paper pattern will reverse to make both. To save foam (I didn't know exactly how I was going to do everything at the time) I cut the tail out separately but you could include it in the body pattern.
It turns out I'm about 6.35 times taller than a 1970s GI Joe doll so once I had a correctly-proportioned copy paper shark I simply took it to pieces and scaled them up 6.35 times on to huge sheets of paper.
Although the first couple of paper sharks were drawn freehand, once I was satisfied with the shape and size relative to the doll I flattened out the pieces and scanned them into my computer. I then traced out a neat version in Adobe Illustrator - I've attached it as a SVG file for anyone that can use scalable vector files. I scaled it up in Illustrator and drew it fullsize using a large plotter. If you don't have a vector application then open the file in your web browser - you could print it at A4 or US Letter and then scale it up, either drawn by hand using a grid or maybe something like an overhead projector. It's a simple shape so you could simply draw it fullsize by eye. The gentle curve along the top of the back (where the dorsal fin will go) is the most important bit as this gives the 3-D shape to the shark's body when the halves are glued together.
Repeat the drawing process for the two pectoral fins and the dorsal fin. You could include the tail at this point but I haven't included a plan for that as I measured up and drew it by hand once the main body of the shark was glue together so I could get the shape and size I wanted. If you have a big enough sheet of foam you could simply include the tail as part of the main body halves but I had to place it on the foam separately.
Finally, draw out the pattern for the u-shaped 'muzzle' area.