Historically, greenhouses were used exclusively by emperors and kings. Emperor Tiberius owned the first greenhouse, a structure built out of thin mica panels to grow cucumbers for the emperor year round. Today, thanks to the low cost of plastic, almost anyone can build an inexpensive greenhouse. A simple greenhouse structure such as a PVC hoop house is so easy to assemble that they are used both for commercial and hobby greenhouses.
Select a location for your greenhouse that has well-drained soil and is in full sun.
Measure and mark the footing for your 12-foot wide and 24-foot long greenhouse using a tape measure. Pound stakes into the ground at the corners. Tie string between these stakes to mark the wall locations.
Pound 3-foot lengths of rebar into the ground 1/3 of the way, 4 foot distances along each wall. For a 24-foot long greenhouse, you will use 7 stakes for each side.
Slip the end of a piece of 24-foot long 3/4-inch PVC pipe over each rebar stake on one side of the greenhouse. Flex the pipe downward and slip the other end over the stake on the other side of the greenhouse across from the first stake.
Stretch a piece of 9 gauge wire between each PVC pipe by wrapping the wire around the end pipe at the summit of the arch. Then run the wire over the top of each arch down the length of your greenhouse. Wrap the wire around each pipe 1 turn before continuing to the next pipe. Keep the wire taut, but do not pull it so tightly that the PVC pipe leans as you pull it. Wrap the wire around the pipe at the other end of the greenhouse to secure it in place. The wire will add stability to your frame.
Place a 24 foot long 2 by 4 board against the stakes along each side of the greenhouse.
Cut a 24-foot long 2 by 4 board in half. Place each half of the board at the ends of the greenhouse. Nail these pieces to the 24-foot long boards where the ends meet to form abutting joints. When you stretch your greenhouse plastic over the frame, you will staple it to the boards at the base of the greenhouse.