Take a look at these guys.
I have used them for other pojects and have been happy with their products. You buy the fittings and the tarps you need and the pipe from your local hardware store. Their fittings fit standard EMT and Fence pipe sizes so you can pretty much create any custom shelter you want. I have a standard 10 x 20 over the Boler
beside the garage but ended up with a big rip in the roof from a heavy snow load this year. Also the bunggies don't seem to hold up in the New England cold. The four season garages use a heavier tarp and the continuous ground to roof to ground tarp will handle the load better.
Since mine is right next to the garage, I am considering using parts to turn it into a lean-to type so the All of the snow and water goes away from the house. For those of you with spare time on your hands you might talk a look at this bow house structure. The truss system is very strong for the light weight