Greenhouse, Noun: a building, room, or area, usually chiefly of glass, in which the temperature is maintained within the desired range, used for cultivating tender plants or growing plants out of season.
When folks think of greenhouses they get visions of large structures made of steel and glass. You can build them that way but you don’t have to. Basic parts include a frame, cover material, floor covering, temperature control devices, and of course a place to put it. A quick internet search will reveal a wealth of information.
Some questions need to be answered before you start construction. How big do you want it to be? How much sun and shade will it get? Will a structure alter the drainage of the existing landscape? Is there enough room for maintenance of the greenhouse and surrounding landscape? What are you going to grow and what’s your budget?
Frames can be made of wood, PVC pipe, and metal such as conduit and angle steel. I have also seen a .5 inch steel water pipe with fitting used. I find wood the easiest to work with as long as you don’t want it round. PVC is the least expensive but you need primer, glue, and a good plan as the glue is unforgiving. Metal frames are the most durable, the most expensive, and for me the hardest to work with.
Cover materials include poly sheeting, Plexiglass, real glass, and sun-blocking fabric. The poly sheeting is the most widely used and is the most cost-effective. It is available in several thicknesses and UV ratings. Sunblock fabric is a must and it also has UV ratings.
Almost any type of flooring is superior to dirt. Concrete slabs, asphalt, stepping stones, gravel, and mulch all work well. I consider concrete and asphalt out of my realm for a backyard greenhouse. But stepping stones, gravel and mulch work very well.
The last area is the temperature and humidity controls. If you are using a greenhouse year-round this will be your greatest expense. Wintertime heating is easily accomplished with propane or electric heaters. But since we have more hot days than cold days we need to think about air conditioning and shade cloth. Shade cloth is inexpensive but is not as effective as A/C. Whatever way you choose, plan your work, and work your plan.