Greenhouse kits are readily available and are seriously the most convenient way to build the best greenhouses with the least amount of energy expended. They come with a frame, panels, and a door. You just have the prep the ground for construction, and away you go, an easy greenhouse garden ready for your plants.
Building your year round greenhouse will certainly require more energy on your part. Although you can find greenhouse plans on the internet, you’ll want to double check that the construction and materials are up for the snow loads in your climate & environment.
Of course if you decide to go the DIY greenhouse route, you can make sure it’s insulated the way you want, it’s perfect for the ground you’re working with, and it allows just the right amount of light for your favorite plants! Just make sure you get started in the spring so you’re ready long before winter gardening comes around. Greenhouse kits do make install much easier.