Tracey, your GH does look awesome! I was just trying to keep you from making some of the same mistakes I did when building a GH from scratch. I do like how you did it! Careful you do not fry your plants with just that one small vent window though. I have a squirrel cage fan to pull the heat out. You know the furnace fans. Move a lot of air. It could not keep up and temps were getting up to 105 in the GH. So I removed two walls to keep the temps from getting higher than ambient.
When I get to MN we have plans to put on a glass sun room so I can grow some plants out there. Along with my basement grow room I will be building. I can't wait to get started with that!
And Sure i would love to chat with you and share some of the things that I have done that I like or don't like. Might save you a little money and time. My yahoo name is JB_Orchidguy. You can also PM me telling me your ready to talk about it. Because obviously there are a lot of different glazings with different R factors and heating methods too.
BTW If you double the plastic with an air gap in between then you will have a little better insulation than just one layer. You would be surprised how much better it keeps in heat.