Although you can purchase expensive kits for constructing a greenhouse, creating an effective greenhouse is just as easy---and a lot less expensive---with the use of cattle panels. Also called stock panels, cattle panels consist of a stiff panel of interlocking galvanised steel rods that provide an ideal curved framework for a small greenhouse. With a single cattle panel measuring approximately 16 feet long by 54 inches tall, you should be able to use two panels to build a 5-foot-wide-by-9-foot-long single-family greenhouse in just a couple of days, provided you collect all your materials ahead of time.
Lay the two 9-foot-long 2-inch-by-4-inch framing boards on the ground parallel to each other. Turn them on their narrow sides and move them until their inside edges are 5 feet apart.
Position the two 5-foot-long 2-inch-by-4-inch framing boards perpendicular to the 9-foot framing boards to create a 9-foot-by-5-foot rectangle. Turn the 5-foot framing boards on their short sides. Make sure the ends of the 5-foot framing boards are flush with the ends of the 9-foot framing boards before screwing them together with 2 1/2-inch galvanised screws.
Lay one of the 2-foot-long 2-inch-by-4-inch boards diagonally across one of the frame corners and nail it into place to strengthen the greenhouse frame. Repeat this process for each corner.
Pull the short ends of one of the cattle panels together with a helper to create a u-shape. Position one short end of the curved cattle panel on each long side of the greenhouse framework, locating one corner at each of the two front corners on the framework. Nail the cattle panel to the wooden framework with 1 ½-inch fencing staples. Repeat this process with the remaining cattle panel, overlapping the top edge of the panel with the bottom edge of the previous panel by approximately 2 inches.
Lay the two 6-foot-long 1-inch-by-4-inch boards parallel to one another on the ground. Lay the shorter 1-inch-by-4-inch board perpendicular to them and nail it to the two long boards to create a u-shaped door frame. Stand the door frame upright in the centre of the front opening of your cattle panel greenhouse and nail the bottom ends of the 6-foot-long 1-inch-by-4-inch boards to the 2-inch-by-4-inch bottom framing board to create your door opening. Nail the sides of the door frame to the bottom greenhouse framing with the remaining 36-inch-long 2-inch-by-4-inch boards.
Spread greenhouse plastic across the back and sides of the curved framework, stapling it to the wooden framework with a large utility staple gun. Position a staple every 3 to 5 inches to ensure that the plastic is firmly attached to the greenhouse frame. Secure additional greenhouse plastic across the front side of your greenhouse, leaving only the door free of the plastic. Install a latch and set of hinges in the door frame and hang a lightweight screen door to provide an entrance. Duct tape greenhouse plastic to the inside of the screen during cold weather to prevent the cold air from entering your greenhouse and damaging your plants.
Mark Freeman, author of "Gardening in Your Greenhouse," suggests that you cover your greenhouse with 1 or 2 layers of 6-mil plastic sheeting, a sturdy greenhouse covering that typically last 3 to 5 years before requiring replacement. (see reference 2)
Exercise care when bending the cattle panels to ensure that they don't spring back and injure you.