Hi Alex... well you've got two obvious ways to go: "Tom Sawyer" or "South Pacific". The first thing to pop into my mind were telephone pole sections lashed together with 1" hemp; a barge with a hut on it. But, when you think multi-hull you've got to consider Polynesian vessels; I can't find them now but Wooden Boat occasionally features lashed boats from the South Pacific. If it were my project I'd build some kind of whacky catamarand or pacific proa with a crab claw sail.