Greenhouses are an economical and effective method to grow plants in almost any climate. Greenhouses can vary in costs depending on the material used to build them. One way to build a low-cost greenhouse is to build it out of old windows. Windows can be recycled and used to generate heat through their glass panes.
Collect old windows being discarded from construction jobs, demolition jobs and old buildings. Make sure the glass is in tact. Try to get pairs of windows if possible because you can use one of the pair for each side.
Lay out the windows along side each other on the ground. Set up four walls with the front and back matching and the two sides matching on the ground. Use each window pair to fill in space on opposing walls (front and back, or the two sides). Remember that one side needs room for the fan and the opposite side needs room for the door. Small holes, gaps and minor height variations can be filled in with wood.
Use the 2-by-4-inch lumber to build frames around the windows. Frame each window within the wall with 2-by-4-inch lumber. Set up the lumber with the 4 inch sides facing the sides of the windows. Connect the wood to the windows with the screws; drill the screw down to where the head is even with the wood.
Set a stake at one corner where the greenhouse will be placed. Measure off one side and set another stake at the end of the tape. Measure off the parallel side to the second stake. Set the third stake. Repeat the process until you are back to the original stake. These are where the 4-by-4 posts will be put into the ground.
Dig the post holes to a depth of 14 inches. Put the square cinder blocks at the bottom of each hole. This ensures the corner posts will hold the green house stable. This ensures the wood base remains intact. Set each 4-by-4 post into a hole. Backfill around the post to the top of the hole. Tamp down the dirt.
Set up a wall between two posts with the matching length. Drill screws into the wall at the base and the top to hold it in position. Repeat the process for the remaining three walls. Set the level on top of each wall to make sure they are straight; adjust any wall by unscrewing it and realigning it. Drill additional screws into the walls to secure them into the posts.
Put the rocks down inside the frame to form the floor. Get the rocks as close as possible. This creates drainage and heat retention for the greenhouse.
Set the metal roofing over the frame. Leave a 6 inch overhang on all sides to keep the rain and debris away from the walls. Screw the roofing onto the top of the walls, Make sure to overlap each roof section to help seal the seams between them.