I raised chicks outside in Virginia one summer, in a dog kennel covered with hardware cloth, with a tarp over 3/4 of it and a heat lamp inside. It worked pretty well. (They went outside the day they arrive at the Post Office. The space was 4 x 6 feet, and I think there were 15 chicks, with no losses.)
I would probably put the heat source in the crate, put the crate against the house, and put cardboard along 2-3 other sides of the crate. (If heat lamp, do not cover the top of the crate. If a different heat source, put cardboard on top of the crate too.) After a week, remove cardboard from one end of the crate, and start leaving the crate door open so the chicks can go in and out. Watching where the chicks spend their time, and where they sleep, will tell when to remove the rest of the cardboard, the heat source, and the crate.
I suggest cardboard because it's usually easy to get, and because the space is under a roof, so cardboard will probably last long enough for this purpose. A tarp could work just as well--it just needs to block wind from blowing through.