If you look at greenhouse kits that are available on the Internet today, you can expect to spend thousands of dollars. One solution that some do-it-yourselfers have undertaken is to build their own lightweight hoop houses. But a hoop house may still cost hundreds of dollars in PVC and wire. For a smaller greenhouse that costs even less, you can build an inexpensive frame by repurposing cattle panels.
Cut the the 2 inch by 4 inch board into three, 8-feet-long pieces. Trim one of the 8-feet-long pieces into 2 lengths that are each 4 feet long.
Nail the cut down board into a box with abutting corners. The box should be 8 feet long by 4 feet wide. This will be the foundation of the greenhouse.
Bend the two, 4 feet wide, 16 feet long cattle panels into U shapes. Place the cattle panels inside the wooden foundation and nail the panels to the foundation with fencing staples.
Place the plywood sheets against the ends of the greenhouse frame so that the short end rests against the ground. Trace the frame of the greenhouse over the edge of the plywood.
Cut the plywood in a U shape along the tracing of the greenhouse frame. Your U shape should be 8 feet tall and 4 feet wide at the base. Cut a doorway into each frame that is 2 feet wide and 6 feet tall.
Place the plywood ends against the greenhouse and attach them by nailing the cattle panels to the plywood using fencing staples.
Attach storm doors over the plywood using the enclosed storm door hardware.
Cover the greenhouse with greenhouse plastic. Staple the plastic down around the base of the greenhouse and the edges of the plywood ends.