I actually had the framing for the walls and roof done by a contractor. I ordered the duel-walled polycarbonate panels from somewhere, and the metal channels. Then there were all the self-tapping screws made for the plastic. I don't remember where I ordered it all from but 15 years ago the panels were over $100 each. I put them all on myself while my husband was at work, lol. Then I built the shelves and two tiers for maximum space.
I will tell you that I do love having it, but I only use it for two months and then it is way too hot inside even with all the fans and the doors open. I start all my seeds inside under lights and in March move them out into the greenhouse which has to have milk house heaters to keep it around 50°. If you are not going to be raising a lot of plants perhaps a domed raised bed would be better and then you can plant in it when the weather warms up.
I use hoops over my large bed and if needed can run a heater inside just to keep it from freezing. Here are a few pictures of mine which is 16' x 8' x 12'. If I remember correctly it was over $2500 15 years ago.
I hope this helps with your decision. Here is a link to a cold frame with cover.
Thanks for all the info @sunscape more involved to make one of these than meets the eye.
I really don't need a big one like you say.. I'll check out the cold frame and hoop house videos. Just one thing, well 2 things , what kind of floor do you have and is it fasten down so as not to get blown about.
The floor of the greenhouse is the ground covered with landscape fabric. The entire thing sits on top of a base frame that was secured with large re-rod placed deep into the ground and then bolted to the base frame. It is never going anywhere, ;-) I wonder if you could have one shipped to you for a lot less and put it together yourself. Worth checking into.
Thanks @sunscape Just wondering how you did it. Many ways , just have to make sure it doesn't blow away..