Got a couple suggestions.
Most of my trees are in plastic pots. (freezing won't break plastic pots)
With trees that are native to Illinois & Wisconsin, and areas further north. Just "Set 'em Down on da Ground". I used to worry about winter sun or winter shade, for most it really don't matter. Take the pots off the bench, set 'em down, and forget them. This is with trees hardy through zone 5 and into zone 4 or colder. Trees that this has worked well for me include Ponderosa Pine, Larix species, JWP, Thuja occidentalis, Spruce - including colorado blue, engleman, oriental spruce, and Black Hills spruce. Amur maple, Acer ginnala, and northern sourced red maple, Acer rubrum. Parthenocissus, Malus (flowering crab), Amelanchier (serviceberry), Hinoki cypress (Chamaecyparis obtusa). Large leave cultivars of flowering quince (Chaenomeles), Bur Oak, Quercus macrocarpa, Many native and introduced elms, Ulmus. Blueberries - highbush types, blueberries low bush types. The list goes on and on. Note: all on this list are native or survive well at least 100 miles north of me. Just plop it on the ground is good with hardy material. Marginal species you have to do something else.
Note, the trees above will be fine. If they are in fancy or not so fancy bonsai pots, there is the chance the pot will break from the soil mass expanding. Make sure the shape of the pot allows the frozen soil mass to lift as it expands. Walls of pots should slope out as they go up, then the soil mass will rise as it freezes. Walls that curve in will lock the soil mass in place and even high quality supposed "frostproof'' clays will break. So if you have trees in fancy pots, evaluate the shapes of the pots before you risk leaving the good pots out for the winter.
I am fortunate enough to have a well house that is not in use. It was built like a root cellar, the floor is 5 feet below ground level. It is covered by my concrete patio, and I have a trap door to get into it cut through the foundation of the house. It stays between 32 F and 40 F (0 - 4 C) all winter long. THis is where I winter marginal and tender trees. This is also where trees in expensive pots go for the winter.
You can get away with an unheated garage, or even a tool shed. It you don't put the trees in until after the ground freezes, and get them out in early spring, you don't have to worry about light, just make sure they don't dry out.
But more an more I try to only grow species that do well in zone 4, which is colder than my zone 5b climate. This way, I don't have to hustle them around in autumn and spring. Just down on the ground.
My well house for winter - no lights, include Satsuki azalea, Japanese black pine, & anything in pots worth more than $100.
