Change the hardiness zone where you live
The U.S. department of agriculture has mapped the U.S. in hardiness zones and, depending on your zone, plants are either annual or perennial. However, with minimal effort and great satisfaction, many annual plants can be perennial
Amaryllis and Mexican Petunia are just a few that will winter over if heavily mulched and bloom in the garden year after year
Plants like Bird of Paradise, Geraniums, Palms, Angel Trumpet Banana and many others can be brought into the greenhouse and then placed in the garden again for another spring and summer of blooms
A greenhouse can be constructed almost anywhere to simply extend the growing season or to provide for year round gardening.
A simple 2X4 construction covered with 6 Mil greenhouse plastic is adequate. A southern exposure is key; the north side can be solid with insulation. Made air tight as much as possible, on a clear day inside temperatures can climb 50 to 60 degrees higher than the outside. There is a lot of information and ideas on the internet. Google and YouTube search Passive Solar Greenhouse
Water containers collect heat during the day and release it slowly throughout the night. The containers can be used to support shelves and tables. Large potted plants also store heat and help to stabilize the temperature. This passive heat system can protect plants even when temperatures reach 15F. I am happy to take questions and comments.