Some tips for building an inexpensive greenhouse include finding free materials on Craigslist or other online sites, visiting garage sales for inexpensive items, and recycling materials from old sheds or barns. Painted water jugs or barrels help to absorb heat without the price of expensive heaters.
Before planning or designing a green house, visit Craigslist, Habitat ReStore and Freecycle for deals on glass windows and doors. Keep an eye out for gravel for the foundation. Go to auctions, garage sales and savage sites for any items not available online.
Use double-paned windows when possible to help the greenhouse retain heat. If there is access to an old shed, remove the aluminum to form the top of the new greenhouse. Design the greenhouse around the items available.
Paint barrels black, fill them with water and line them up around the sides of the greenhouse so they can absorb heat during the day and release is at night. Another way to manage temperature without spending extra money is to build the greenhouse against one's own house. This lean-to greenhouse not only absorbs heat from the shared wall, but it also has a structure that requires only three instead of four walls, another money saving method.