If you have a bunch of old glass windows lying around (or available at a nearby thrift store), upcycle them into a beautiful ...

Alternatively, you can make a greenhouse from old windows without using these other elements, as their frames can be joined ...

Plastic sheeting is used as a covering to help let in plenty of light while keeping the cold out. The greenhouse is also heated, and can maintain a 40 deg F temperature differential with 14,000 BTUs.