To build a greenhouse, you need wood, UV resistant polyethylene film, plastic or fiberglass frames and galvanized nails. The type and size of the greenhouse is determined by the set budget and available space.
First, evaluate the site where you want to build the greenhouse. Ensure the site gets adequate sunlight. If the site is below a slope or hill, put in a drain to redirect any water flow away from the greenhouse site. Additionally, the site should be level or in a place that can easily be made level. Determine the dimensions of the greenhouse and the length of water pipes required. Count the number of frames needed for sidewalls, roof and base.
Begin by constructing the base with timber or plastic frames. Lay the wood or plastic frames on the ground securely, in the size you have chosen. Fix the timber together, using nail plates or galvanized nails. Next, construct the sidewalls by fixing fiberglass or plastic frames on the three sides first. Ensure the walls are firmly attached to the base, and then join frames with the three sidewalls using nails and adhesives.
Fix an entrance frame and window on the fourth side, and put hinges on the door and window with the adjoining frame. Cover the whole building structure with a UV-resistant film. If necessary, install electrical fittings on the sides, and lay pipes for the water supply.