Also if you decide to opt for a much bigger brooder (6x6 vs 6x3 for example), for the first few days to a week or so, you might want to add an option for a temporary "wall" to reduce the size of the brooder by half, to prevent chicks from wandering off too far from heat, food and water. Something as simple as cardboard securely taped in place would do. It's unlikely that they can't manage to find their way around 36' sq ft, but newly hatched/veyr young chicks are more susceptible to getting chilled/lost/etc.