We are planning on ordering about 20 Cornish crosses this spring. What size brooder do they need week to week? We have a dirt floor barn with 4 11.5'x8.5' stalls. I was thinking a plastic kiddie pool with a heat lamp for the first few weeks then just use the heat lamp in the corner of a stall without the pool and finally moving them out to their chicken tractor in the yard. Thoughts?