When we started our baby chicks, We simply use VERY large card board boxes as the brood boxes and covered the top with hardware cloth. As they grew bigger, We connected several cardboard boxes (draw a square on the sides of two boxes, about 2-3 inches from the bottom -make sure the sqaures match. Cut top/down edges of one box, and left/right edges of another box, you can then form a tunnel between two boxes) for them to run around. The top is only covered with hardware cloth - they need the ventilation, and we can see them). After they migrated to the real coop, we simply threw out the boxes! No need to buy plastic crate (big ones are expensive).