An idea I’m working on for a shipping container home. Two 40 x 8 containers deconstructed each side forms a welded wall of the new structure set on a base of sufficient depth for your area.
The center is poured concrete. he solid walls a re welded end to end to form the box. Engineered steel beams form the roof which gives you an enclosed area 40′ by 40′.
The other four door areas left over from dismantling to get the four walls could be used to form a garage door opening, or two openings. You would need some structural steel to weld in to replace what was taken with the side doors, but at the end you would have a solid set of doors to your garage.
Nothing is to scale, but you get the idea. Pretty cheaply built and encompassing 40′ x 40′. Solid, spray foam to combat or eliminate the condensation problems steel buildings have and you have a pretty good home.