Decide where on your house or building you want the lean-to greenhouse to be constructed. Place the greenhouse near a door and an electrical outlet if possible. Ensure that the location of your lean-to greenhouse gets at least four to six hours of direct sunlight each day, even in winter.
Measure the foundation for your lean-to greenhouse with a measuring tape. Mark the corners with stakes.
Dig 8-inch deep trenches for three pieces of 8-inch thick by 8-inch wide lumber for the foundation of your greenhouse. Each piece of lumber should be as long as one sides of your greenhouse.
Frame your walls with 2 x 2 lumber.
Use a screwdriver to attach a 2 x 2 board the width of your greenhouse to the side of the building you are putting the greenhouse on. This board should be 8 to 10 feet off of the ground. Frame the back wall around this board.
Frame the front wall so that it is 6- to 8-feet tall to allow water to run off of the roof of your lean-to greenhouse.
Add boards to the side and top of your frames to create a support structure for your greenhouse. Each vertical board will need to be angled to fit the slant from the back wall to the front wall of your lean-to greenhouse.
Cut wire mesh to fit the roof of your greenhouse structure and use a staple gun to attach it to support the greenhouse cover.
Attach polyethylene panels or plastic sheeting to the top and sides of your greenhouse with nails or staples. Overlap the seams of your greenhouse cover to seal it tightly. Leave space on the front or side for a greenhouse zipper door or wooden door.
Attach the greenhouse zipper door or wooden door according to the directions on the door.
Put plants inside your lean-to greenhouse. Water plants regularly.