If you build a solid, secure draft proof coop with sufficient ventilation, they should be fine. Rule of thumb is 4-5 sq. feet per bird inside the coop excluding roosts and nesting boxes, and 10 sq. feet per bird in the outside run. Silkies really don't fly, though they can jump high. They also have crests and beards that obscure their vision so they are much safer in an enclosed run with top. Otherwise they are sitting ducks for predators.
You may want to check out the coops section for ideas, and the predator threads to learn how to safeguard coop/run. You could also check the "Silkie thread," to see how others get their birds thru hot & cold weather.
My Silkies do great in the winter. I don't provide them with additional heat or anything special. They're actually my cold weather superstars, and are usually the only birds laying. However, right now, its about 90F outside and they're suffering. Everyone is laying around in the shade panting or running to the drinker. This is the time of year I do special things for them. Today they got a frozen watermelon. Yesterday they got a couple of cans of frozen corn (I freeze the corn in the water its packed in and drop it in a shallow bowl of water). I'm getting 0 eggs from them right now. In their defense, most of them are sitting on eggs or raising chicks, but still.
They're actually pretty hardy little birds, keeping in mind that they're very susceptible to predators.