Here's an awesome DIY cattle panel greenhouse design from Alan (aka TexasPrepper2) at HomesteadAdvisor.com. It appears to be simple enough for a single person to construct in less than a day and yet is sturdy, functional, and even looks great. With just a quick estimation, this greenhouse would cost about $120 to build with all new materials. And if you have extra lumber, nails, screws, etc lying around you could probably build this for next to nothing.
Due to the detailed instructions in the video, it probably wouldn't be too difficult to build this greenhouse without the plans, but I'll probably buy the greenhouse plans as a kind gesture to him for his ingenuity and creativity. If you want the plans or just want to support Alan, he sells his cattle panel greenhouse plans in an e-book on Amazon: (DIY Greenhouse Plans).
According to my (GUESS)timations, I think a person can build this greenhouse with the following materials:
8' long 2x4 (approx 11 pcs) - $35
16'x52" Cattle Panels (2 pcs) - $40
6mm Polyethylene Plastic Sheeting (min. 20'w) - $25
Pipe Insulation Tubes (min 32') - $10
Misc Hardware (screws, staples, hinges) - $10
Please do not quote me on this though as I am only estimating based on materials used in the video and prices in the linked materials may change at any time.
Once you build the bottom frame and install the cattle panels, an unskilled handyman could probably fabricate the rest of the greenhouse as they go along. But just to be safe, I'm going to recommend you buy the DIY Greenhouse ebook listed above.
Growing vegetables in your new greenhouse:
If you've never grown in a greenhouse, you are probably making the same assumption as I did. "WOOHOO! Year round vegetables!" Well, yes, and no. It's fairly hard to manage a greenhouse in the extreme heat as well as the extreme cold.
Most people with small greenhouses like this use the greenhouse mainly during early spring and late fall. There's not too much you can do to keep these small greenhouses cool in the summer aside from using fans and/or covering the top with materials to help filter some of the sunlight. For most vegetables, I seem to do better by starting them indoors, then transplanting them in the outdoor garden after all threats of frost are gone.
The winter time seems to have it's own unique set of problems. During winter, days are shorter and plants don't receive as much sunlight. Even though daytime temps inside can reach very comfortable temperatures during the winter, when the sun goes down, the inside of the greenhouse loses heat rapidly. Many people seem to have found luck double layering the greenhouse with extra plastic. Heating 55 gallon drums filled with water via a solar water heater has had great outcomes. The barrels get heated to 100+ degree water, and then radiates the heat throughout the night. There are other options such as wood burning stoves, and electric or gas heaters, but that tends to get pretty expensive. Snowy climates require greenhouse owners to go out and remove the snow from the tops as well to avoid collapse or damage to the greenhouses.
There are many vegetables and plants that can thrive thoughout the winter as they require less sunlight and arent affected by cooler temperatures. Unless you plan on adding grow lights and maintaining temperatures I wouldn't get your hopes up for year round tomatoes and green peppers however. Some vegetables such as spinach, turnips garlic, cabbage, broccoli, cauliflower, celery and radishes all seem to grow just fine throughout the winter as long as you keep indoor air and soil temperatures above freezing.