advice on idea

i want to start up some clones and grow them at least 20 inches by mid Oct. how feasible would it be to finish them outdoors in a green house considering it would be winter? would it take longer for them to finish?
or maybe not even a green house but a canopy of some sort like a car port but modified?
it's not very well thought out yet to me but I'm just looking for some feed back to help me better understand the cons and pro. if anyone could just shoot out whatever there thoughts are on it it would be helpful. i sure there's a lot of shit i haven't even took in to consideration.:what::twocents::question:

it wouldnt be feasable. they would flower. clones need at least 16/8.

if you keep a good grow light on them 16/8 or more (metal halide) and keep them warm and give them lots of love they will be fine
just dont let them freeze or even frost and when you want them to
flower just turn the lights off and let nature take its course.