I live in the panhandle, and except for an occasional snow and 60+ inches of rain, it is humidity and heat. I bought a previously owned 70s ranch and delegated the living/dining room to be the train room. That gave me a 28' by 14' around the wall layout.
If I was to build, I'd take advantage of today's house designs that favor high pitched roofs. Normally, they use manufactured simple trusses that don't provide any usable attic space. Sometimes, you'll see they use a storage truss that provides a small, open space with ladder access for storage. These trusses are built with 2x4s and provide support for small loads, This space is outside the insulated envelop.
Since you are custom building you can specify what size of attic you want. It will be designed using larger lumber to support the additional loading (sometimes you'll see this called a 1 3/4 story house). Spray foam on the underside of the rood and over the soffits brings the entire attic into the heating/cooling envelop of the house. This is more efficient but costs more. As long as you can handle the stairs, your wide and cars will appreciate it.
Jan
