Gonmon's DIY Greenhouse Plans

[Gonmon]

Of course we all want a greenhouse, but for some of us a prefab kit just won't do. I always try to DIY whatever I can to save money, because I can tailor it to suit my needs, and it usually costs a lot less. After reading a bunch of books and spending hours (days?) on the internet I've came up with a plan I want to show you all.

This greenhouse is 12 feet wide and 16 feet long, with the peak running East-West. The top of the peak is 12 feet from the foundation. The two ends (West and East sides) are walls out of 2x6 pressure treated lumber, studs spaced 24" on center, with exterior grade plywood skin on the inside and outside. Although the East side would only have plywood 3 feet up, the upper part would be glazed to let in morning sun. The ribs along the North and South sides are either 3/4" EMT metal conduit, or 3/4" PVC pipe. The length of each rib is ~14' with a radius of ~14.5'. I think I could attach the pipe to the wood frame with angle irons bent to the right angle, with the pipe slipped over it? The South face would be skinned with a double layer of poly inflated with a fan. The North side I want to skin with something opaque and insulate. I also want to insulate the bottom 3 feet of the East and South sides. I don't know what I'd use to insulate the curved walls.

It would be mainly for orchids (Stanhopeas, bulbos, mini-catts, etc.) but I also grow carnivorous plants, tropical fruits, and maybe some fresh veggies for winter. I want to start breeding and need more space for large stock plants and raising young plants than I have room for indoors.

Unfortunately I can't seem to get my images inserted... so they're attached. First pic Southeast view. The white rectangle above the door is the vent. I need to frame out a spot for the exhaust fan on the other side once I determine what size fan I need.

Second pic, birds eye view, northish. The white space is all fixed benches, the red space is a movable bench, if I can figure out how to do that. The green box is an aquaponic system. And the orange cylinder is a water heater. I haven't ran the numbers to see if I could heat it with a household water heater, but if I can I could run hot water through the floor of the greenhouse.

Third pic, South view.
Fourth pic, East view.

The big blue boxes are water storage tanks, maybe. Originally I made plans for a conventionally shaped greenhouse with gutters to collect rainwater, but with a greenhouse this shape I don't think that would work. My tap water is very hard so I would have to filter and treat it to make it suitable for the things I'm growing, or use RO or rainwater. Watering out of tanks inside the greenhouse would have the benefit of storing heat, and the water wouldn't be cold going on the plants. The benches will sit on top of 55 gallon drums filled with water, for heat storage.

Areas: insulated - 433 sqft; double wall polyethylene - 160 sqft; twin wall polycarbonate - 59 sqft
Volume: 1522 cuft
Using a $2 price per gallon for LP gas, a minimum inside temp of 65F, and avg outside lows for Mishicot WI 54228, I calculated this greenhouse would cost around $500-800 to heat over the winter. That's not counting any heat storage, or night-time insulation over the glazed areas.
The fixed benches equal roughly 70 sqft and the movable bench 24 sqft.
If a 16 foot treated 2x6 costs $8.50 and a 10' long 3/4" conduit pipe costs $3.30, the greenhouse frame would cost just $200. Plywood would add about $125. Then gotta add glazing, insulation, heater, etc etc. I might be able to build this for less than a grand?

Things I'm not sure about:
Would I have to brace up the East and West walls?
How to attach the poly to the wood frame?
How to attach the exterior siding on the North side?
What insulation would I use on the North side, and the bottom of the South side? Spray foam insulation would work best but cost effective?
What to do for a foundation? Was thinking of a 12'x16' frame of 2x6's with 4x4 posts at each corner and every 4 feet on the sides.

So what do you think? I know I still have a lot of work to do yet.