Hi Mini Meat!
This experiment is still ongoing... The chicks are a little over 2 weeks old right now and still going strong. I had to try this as I live offgrid and don't have enough power to run a heat lamp all the time. But it has been working amazingly well for an experiment I didn't think would work (I was taught that chicks could not survive without a broody momma or a heat lamp) but I've sure shown that that isn't the case.
I started out with a small cage about 1'x2'x1' then I added a draft barrier around it that was about 5" tall. The food and water is in the cage area (1'x1' area) and I made a 'mini coop' for them to warm up in that was also 1'x1'. The coop is a cardboard box lined with emergency space blanket foil, and then chopped straw was added until it was 1/2 full. There is also foil under the lid of the box that is attached at the top of the front of the box. And it drapes down to the back where it rests on the straw. There is a chick sized hole in the front of the box so they can come and go as they please.
This setup is in an uninsulated workshop with a small wood burning stove that is lit at night to keep the temp around 40* F. Other than that there is no suppplemental heat. The chicks were maybe 2-3 days old when I got them, and with the 4 that I have (2 white crested black polish, cuckoo marans, Easter Egger) they cuddled to keep warm. So far they are at least 50% feathered out already, they are a tiny bit smaller than they would have been under a lamp. But from the research that I've done they should catch up in size once they get big enough to go outside.
I hope that helps, if you have any more questions please ask!