I have 2 light brahmas that are 22 weeks and 1 of 2 just started laying. The are HUGE and at 22 weeks easily outsize my 2 year old RIRs. The pop door is 12 x12 and it seems fine. I agree about keeping the roost on the low end to prevent injury when jumping down. They have not had a problem getting of roost of 2-3 ft