I was assuming a solid floor to the "all wire" brooder. With a heat plate to hide under, and some bedding underneath, I would expect the chick to be fine. If there seem to be drafts, it could make sense to put cardboard on some sides of the cage during the first week or so, then watch the chicks' behavior to decide when to remove them.I just felt bad picturing 3 newborn chicks in a wire cage in the middle of a garage. Maybe if he posted a picture it wouldn't seem so cold. I'm in Wisconsin vs. Florida, so big difference there too!
If the brooder really does have a wire floor, then putting something on the floor is a good idea, so the chicks have a surface to keep their bellies warm as they sleep. A piece of cardboard or wood can work for that, preferably with some bedding for them to snuggle into while they sleep.