Many gardeners would like to have a greenhouse to extend their growing season, but can't afford the high cost of a commercially bought greenhouse. With some effort and creativity, you can build your own greenhouse that can provide you with the same benefits of a commercial greenhouse at a fraction of the cost.
You can build a greenhouse using PVC pipe and sheets of plastic. PVC pipe of 3/8-inch diameter is flexible enough to bend into semi-circles, creating a framework for a Quonset hut-style greenhouse that can be covered with plastic. This type of greenhouse can be built in nearly any size, and will hold in a surprising amount of heat from the sun, given that its walls are made of a single sheet of plastic.
A more permanent and durable greenhouse can be built out of sheets of glass, although this requires more work than a plastic greenhouse. Storm windows and used windows are widely available through architectural salvage yards, used building materials stores and private individuals. Many people simply throw away or give away their old windows when they replace them with new, insulated windows. Old windows can make very effective greenhouses, particularly if you are able to acquire a large number of windows that are the same dimensions. Build a framework to hold the windows, install the windows, and you have a nearly free greenhouse.
A cold frame is essentially a miniature greenhouse. A cold frame can be constructed by building a wooden box with an open bottom and a top that is tilted toward the sun and covered by a hinged window. Put the cold frame over seedlings in the garden, and the effect is the same as if they were in a greenhouse. By hinging the window on top of the frame, you enable yourself to lift it up to tend the plants inside the cold frame.
You can make a greenhouse that can double as a pleasant sitting room by building a glass-covered addition to the south side of your house. This saves money because the back wall of your greenhouse is the wall of your house, so is already built. By building the rest of the greenhouse using salvaged and used materials, you can save even more money. This arrangement also makes greens that are growing in your greenhouse easily accessible from your kitchen.