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.