I thought this might make a good first Instructable after the amazing reception it got at Spiders Nightclub's Halloween Party. I'd wanted to do something like this for a couple of years but never got around to it in time for previous Halloweens. It took a few days but most of the time was looking at shark pictures on Google and making little paper maquettes of the shark to try and work out scale and construction. I used an Action Man (GI Joe in US) doll to get human proportions but everything would be much easier if there were two people involved so you could measure up on a live model. By the way, I am very old so a trip to some old boxes in the attic dug up an Action Man of early 1970s vintage. I believe Action Man/GI Joe nowadays would only be useful for pattern making if you are a giant steroid-filled bodybuilder.
I would highly recommend getting a friend to help whenever you have to try the pieces on for fit, it'll save a lot of time. I'm the kind of person who visits instructables a lot and thinks that spending the week before Halloween building a large and impractical costume is a better idea than going out and talking to people so consequently I have no friends to help out.
All the proportions and patterns are designed to fit a skinny person like myself, not much of a meal for a shark! YMMV.