So this is going to be my 1st winter with my bonsai and I have an idea of what needs to happen but some additional information would be nice.

Bonsai:
1 Chinese Juniper
2 Japanese Maples
1 American Elm
1 Gingko
1 Black Pine

I know that some of these will need to be winterized or put somewhere they can be away from the cold. I live in upstate NY and its gotten do to 40F a couple nights so i know the cold/frost is coming and trying to see what to do.

Do they to be surrounded by something to keep them warm? Do they need less light? Just basic needs

Right know they are on my roof with a half-greenhouse enclosure and they have been great so just trying to keep the trend

this is also my first winter and i primarily have strong trees that can handle the cold(taxus). they need less light to start hardening, that's all i know.

well first thing is you will need to take them out of their greenhouse. even though temps may fall to freezing being in a greenhouse the temps inside can increase dramatically on a sunny day. for your deciduous trees once they loose there leaves they do not need light anymore.
i burry my pots in the ground and cover them with a wooden encloser with one side open away from the wind,this allows snow to get in and cover them. freezing is not the problem it is the drying wind that will kill the trees. the problem with this set up is that rabbits and other rodents will eat the softer growth and bark so ive used small holed chickenwire and surrounded the shelter tightly including the bottom to keep them out
your conifers can be left in the open more .i still bury the pots in the soil but they will still need a sparce amount of light. i have wood lattice over them to stop the snow from crushing stuff. living east of buffalo,ny 4 feet in a few days isn't unheard of
as for your gingko i dont have one so i really can't give advice

Would putting the trees in an unheated attic work? There is minimal light for the pine/juniper and the others could be away from light/wind. Also would it be ok to just recover the greenhouse with black out screen so there is less light?

The greenhouse has some ventilation but i think i could close it off all together from the wind..

I sadly am not able to bury the pots or i would do that for sure, living with limited space sucks, just trying to see what i can do to make these survive.

I randomly saw on jeopardy that gingko lose all thier leaves on one day but thats it

if there is some light in the attic that would work as long as it is cold enough. trees need to be held at 40degrees or lower for a sustained dormancy. the trees will also need to be watered
as for the greenhouse covering it with black plastic will only build more heat inside ,but i guess if it is ventilated enough the heat wont build up too bad with a clear covering