Planning a large freestanding Greenhouse in 6b zone. Need tips for best design.

[atdees]

Planning a year around orchid oriented Greenhouse that would be kept at Intermediate to cool temp range. Looking at at least 20 x 10". I am looking for ideas about wall and roof material. Snow load of 25 lbs minimum. Heating options are either propane or electrical. Need to be prepared for the occasional power outage in the winter cold. I have had a greenhouse before in So Cal but this is a totally different environment in the desert with temps down to 0F sometimes. I would love to see other peoples setups in similar conditions.