Many gardeners are familiar with the large commercial greenhouses at nurseries or garden centers. These greenhouses are designed for large-scale production of bedding plants, and they are very expensive to operate. But you can make a small-scale hobby greenhouse fairly inexpensively using products that you can find at a hardware store. One of the simplest designs for a greenhouse is a quonset design. This is also known as a hoop house or high tunnel design.
Choose a location for your greenhouse that will not be shaded by nearby obstacles, such as your home or a tree. A greenhouse should be located about four times the distance away from the height of any freestanding structure. Remember that the shade line of a structure is deeper in winter than summer.
Mark the boundaries of your greenhouse with spray paint and a measuring tape. A good size for a hobby greenhouse is 12 feet wide by 12 feet long.
Divide the 3-foot rebar stakes into two groups. Drive each halfway into the ground at 4-foot intervals from on both sides of the greenhouse.
Slip the schedule 80 PVC pipe pieces over the ends of the rebar on one side of the greenhouse. Bend the pipe downward and slide the other piece of pipe over the rebar on the other side of the greenhouse.
Cut the roll of 12 gauge wire into four sections each 13 feet long. Wrap the ends of two of the wire pieces around the top arch of a PVC pipe piece on one end of the greenhouse and wrap the ends of the other two wire pieces around the top arch of the PVC pipe frame on the other end of the greenhouse. Bring each wire down a side of the greenhouse over the pipe and wrap it around the base of the PVC pipe frame on the opposite side of the greenhouse. When you have finished, you should have a set of criss-crossing wires on each side of the surface of the greenhouse.
Cut the greenhouse plastic so that it covers the top of the greenhouse and overlaps the ends. Unroll the plastic across the top of the greenhouse. Unfold the plastic so that it drapes down the sides of the frame.
Weigh down the plastic around the bottom of the greenhouse with cinder blocks or pieces of board. When you want to enter the greenhouse or vent the structure, pull an end open to create a doorway or vent.