Look at a steel building. It's been my experience the they are comparable in price to traditional construction, but last longer. You can also have wider and stronger spans in the middle without the need for support posts that can get in the way. You can insulate the interior with basic foam, or build internal walls and fill with traditional insulation. They last a long time.

Personally, twin Quonset huts would work for me, joined together in between by an enclosed pass through, about 8 foot wide. However, I don't think the neighbors would care for the look.

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1987 560SL
85,000 miles