It is very difficult to estimate waste when building the superstructure since many small pieces are cut out of larger ones. Add to that the very broad range of ideas that people have when building the superstructure, and you start to realize that estimating wood for it is difficult. That said, the way I would go about it is to look through the manual and write down the various thicknesses of plywood suggested for the various parts (sides, roof, furniture etc), then make some rough square footage estimates from a sketch of what you'd like to do, and then make your estimate for number of sheets from there. I find that almost always, the trailing end of these types of boat projects becomes a "buy it as you need it" sort of thing ...you can likely come up with a 70% accurate answer for your own project, but trying to get things perfect is likely to fail. If you insist on only using a type of wood that has to be shipped to your location, then I would try to find a local outfit that ships wood from a supplier that also sells what you want and then try to work out a deal that lets you add a few sheets at a time to their regular order ...to minimize shipping costs. OR, find a local supplier of plywood that you can be happy with and adopt the "buy it as you need it" philosophy.
I know this wasn't much help, but it's exactly what I would personally do and what I'd have to do for you if I made an estimate for you ...otherwise, there are no accurate estimates recorded anywhere, including in my own documentation ...and these are the reasons why.
Brian