Measure and mark the foundation of the building with a tape measure and garden hose. Hammer stakes into the ground at each corner of the proposed structure. Tie a string between each stake to make a more permanent guide for constructing your greenhouse and remove the garden hose.
Cut pressure-treated 2-by-4 boards into the correct length using a rotary saw to create a wooden baseboard. With three 2-by-4 boards measuring 24 feet, you can create a greenhouse that measures 12 feet wide and 24 feet long. Screw these boards together using wood screws and a cordless drill at the corners to form abutting joints.
Divide 18 rebar rods into two groups of 9. Place a rod just inside each corner of the greenhouse. Place rods at 3-foot intervals down the length of the long side of the greenhouse. Pound each rod halfway into the ground just inside the wooden foundation using a mallet.
Slip a 3/4-inch PVC pipe over each rebar rod on one side of the greenhouse. Flex each pipe into a U shape and slip the other end of the pipe over the rebar rod on the other side of the greenhouse across from the first pipe.
Place a storm door into the U-shaped opening at one end of the greenhouse. Attach the door at the corners of the frame to the top arch of the pipe and the foundation using wood screws.
Sink two T-shaped fence posts into the ground directly behind the storm door frame using a fence post driver. The T-shaped fence posts should both be on the same side of the door frame. Attach the storm door frame to the T-shaped posts with zip ties. The posts will help to reinforce the doorway and take stress away from the PVC pipe where the door is anchored.
Stretch 9 gauge wire across the top of the greenhouse using a ladder and wire cutters. Wrap the wire around each piece of pipe as the wire crosses the pipe. The wire will help to reinforce the greenhouse frame and give the pipe structure and stability.
Cut aluminum greenhouse locking channels with tin snips so that they are the same dimensions as the greenhouse’s sides and rear. For the front of the greenhouse, cut the channels so that they fit around the storm door and the bottom of the greenhouse on either side. Pull the nesting strip out of the channel. Attach the channel to the wooden base of the greenhouse and the frame of the storm door using a drill and wood screws.
Pull Y-folded greenhouse plastic over the top of the greenhouse. Allow the plastic to drape over the back and front of the structure. Unfold the plastic and allow it to drape over the sides of the greenhouse.
Cut the greenhouse plastic away from the door with a utility knife.
Insert the greenhouse plastic into the locking channel. Place the strip into the channel. The locking channel will pinch the plastic and hold it in place.