Catamaran Modification

I am about to embark on some modifications to an open-bridgedeck catamaran. One project is to build a bridgedeck cabin (yes, the hulls have more than enough bouyancy and clearance will be at least 28'). I am curious to know if anyone has ideas for, examples of, or experience in such an undertaking. This is a custom design that has no lines drawings to work with. If, for example, you know of software which permits a user to import photos in lieau of plans please enlighten me. I'd hate to uglify the boat in the process. Also, I'd welcome a source(s) of current information on suitable scantlings for this structure. I've heard Ron Gibbons' book the Cruising Catamaran Advantage might be useful. Hope the picture loads!

 

If you take pictures in profile, forward and aft, and then use transparency film to draw over, it will show how the changes may look. It is cheap and easy to experiment that way.