We built our greenhouse here several years back. While most of it was made with new materials we did use the squirrel fan and a box fan from an old broken down gh. The wood was new as was all the plastic and pvc. When we built it the new materials cost us about 300 dollars although the price included enough plastic to completely recover the gh with two layers two more times. This project took us one day from start to finish.
Here is a basic photo tour of the gh. Please excuse the clutter. We could really use one about 2x the size. These pics were all taken today rather than as we built it..
If you notice in the pictures, there is a place for a squirrel cage fan. It is used to inflate the layers of plastic, giving it more insulation etc. Ours broke, they are about 75 dollars to replace. We dont have the money to replace it and heck I have been without it so long now, I know it isnt necessary. We also used simple box frame fan for ventilation. With the fan , the door open and the shade cloth we can grow all summer long. You may also see the wood stove in our gh. It worked well but through the year we have figured out that buy using crop cover cloths and mini hoop or frame houses with in the gh it is near as effective and saves a lot of hassle. We no longer use the stove and will be pulling it out soon to make room for a raised bed area.
My advice for a greenhouse is make it operate how you want it to. What works for one may not work for you. Experiment and see just what you can grow in there without having to have all the fancy stuff. If you want to try something new and see if it works go for it. More often then not you can find a way to make it do what you want. You are gaining experience in the process even if you fail, all you have lost is some time and a few seeds. The knowledge you gain will be priceless.
We use the gh pretty much year round. During the winter months, I grow early spring or fall crops. Right now I have turnips, greens,lettuce, mint, thyme, oregano, peas, gr onions, carrots and other salad fixins that we are harvesting from. During the spring and fall months I grow much of our lettuce in there because it has less bug issues than outside. Early spring I use it to harden of plantlings before transfer into gardens. Summer time I tend to throw experimental crops in there just to see if they will grow in the extreme heat(I shut off the fan ). More often than not whatever I plant in there thrives during the summer. The only time I have to worry about any death in the greenhouse is from the end of December til the end of January. By that time I am ready for a break before the spring rush begins and I dont care if it all dies off.
The gh measures 12x16 feet. The ends are framed with 2x4's, the base of the sides are made from 1x4's and the main beam down the center is 4x4.As you can see in the attached pictures, the rest of the frame is made with pvc. (I think the pvc is 1 1/2 in.) At the base of the frame we have u shaped clamps screwed in to hold the pvc to the 1x4's. Where the pvc crosses we used duct tape and then used insulated pipe wrap so make a cushion for the plastic layers. We attached the end layer of plastic separately from the sides and top. To attach the side layers of plastic we used the fabric, duct strap or sewer strap they use these days. we laid the two layers of plastic placed the strap over and stapled.
When you build a green house one of the important things to think about is placement. If possible, locate the greenhouse where it will be exposed to at least 6 hours of direct sunlight during the winter months. The best
Another thing to keep in mind is wind exposure. If you live in an area that is prone to high winds, think about placing it so that an end wall can be built of solid panels on the windward side. Remember too that often times it isn't so much the wind causing the damage but your materials for building the gh were too light for the job. A bit of over kill on the frame is going to prevent a lot of damage. If the frame doesn't hold up nothing will.
Make sure you use gh UV rated plastic. It is expensive but it is well worth it. We have not yet replaced any layers on the gh here. This will be our fifth season with it and barring anything unforeseen it should last at least through this season.