Good luck with them Renee, a bigger box will help a lot. Remind me again how old the chicks are? If you get the coop built and the temps stay in the 60's & 70's they should be fine in the coop. I have my coop with a ambient temp ranging around 60 degrees with a 250 bulb, our nights have been in the minus this past week. My 4 & 6 week chicks are doing great as well as the 4 silkie chicks (under a week old) that have a red flood light that is keeping their area around 80 degrees. At first I had them at the 90-95 degrees, but they got pasty butt. I reduced the temp. and they are doing great. Mine have been out in the coop since day 2 so mine acclimated to the colder temps. pretty fast. They all feathered out a lot faster than the chicks I raised all last spring in the basement. I definitely worry about them that first week, but they are a lot tougher than we realize