I raise my Cornish cross birds on 27% game bird starter from start to finish. With 27% I can raise them in 6 weeks instead of 8. The weights range from 4.5 to 6 lbs in that time frame. I’ve raised meat birds several times doin the 18% feed with off and on feeding I don’t do any of that any more 27% non stop feed out of 25 birds lost one due to heat one to an owl and one for failure to thrive. I use a 10x20 chicken run off Amazon comes with everything you need wire and all. It’s light weight and movable and cheaper than building one of similar size.