Ditto to what Ray said with two additional thoughts.

1. Are you going to get the right air flow with the side vents over two
feet high in the side wall? This configuration may result with most of the
air moving from side vent to roof vent both of which are higher than your
benches and plants. It is nice to have the plants in the direct path of the
air flow, but I do not know if it is necessary.

2. If you find you need to add cooling, the side/roof vents may be very
hard to retrofit with a swamp cooler. Do other orchid growers in your area
use swamp coolers?

Pat