since the std 6 x 6 garage is only 2m high which will likely cause some grief anyway, consider what groper did on the boatdesign.net forum
http://www.boatdesign.net/forums/boat-building/efficient-10m-displacement-powercat-build-thread-38588.html

basically a polypipe hoop structure with plastic roof, cheap as.. Plant it at the door of the garage or make an alternate door. In this way you keep tools and some storage in the garage and build the boat on the infusion table running out through the door from it. Assemble alongside.the table