Going with the fact that most of us don't live on hillsides, there used to be nursery in southern NJ whose greenhouse was an 8' tall concrete block "box" structure - insulated and covered with nicer-looking siding externally, painted white on the interior - with a polycarbonate-glazed roof.
Very energy efficient, and all they did was arrange the brighter plants in the middle, and the shadier ones on the perimeter.