Different structural options
In simplest terms, greenhouses come in two basic styles: freestanding and attached. Freestanding greenhouses allow you to choose the best possible site. Ideally, the greenhouse should receive full winter sun, and its longest side should face south. But because freestanding structures are more exposed to the elements, they can be more expensive to construct and operate. You'll need to have plumbing, a heat source, and electricity installed.
With an attached greenhouse, you'll probably have to compromise on sun exposure. But keep in mind that you can even have a greenhouse on the north side of your house if you're willing to add supplemental lighting or grow plants that prefer shade. If you plan carefully, you may be able to make full use of your home's existing features, including water pipes, heating, and electricity.
Wood is the easiest to use if you're building it yourself. It is strong enough to support glass glazing, but it is also the heaviest and therefore costs more to ship. In addition, you must treat even decay-resistant woods (cedar and redwood) with linseed oil or another wood preservative to prevent rotting in the humid greenhouse environment.
Galvanized steel and aluminum are also strong enough to bear the weight of glass glazing. One drawback is that they may conduct heat and cold.
PVC (polyvinyl chloride) frames are only appropriate for lightweight film-covered structures.
You have numerous choices for glazing including: glass, polycarbonate, acrylic, fiberglass and plastic film. One common misperception is that transparency means better light transmission. The truth is that many translucent materials transmit just as much light as clear glass.
Tempered glass is still the longest lasting and easiest to maintain, making it the ideal choice for sunrooms and solariums.
Polycarbonate and acrylic panels are almost as permanent and transparent as glass. These three materials are more expensive than fiberglass and require a stable foundation.
Fiberglass panels, on the other hand, are relatively inexpensive and long-lasting when properly maintained. But you can't see through them, and their ability to transmit light tends to fade over time.
Plastic Film ranges from transparent to translucent. Some films with ultraviolet (UV) protection can last 5 years or longer. Other must be replaced yearly, so be sure to check on guarantees.