Preface: I live in the tropics, warm weather, year round.
I brood my newborn chicks for three days inside with a heat plate and then transfer them and the heat plate to a bottomless cage on the floor of the coop (not under the roosts so that they don't get soiled as the adult birds sleep). Once the chicks are about two or three weeks old, moving about with agility, I raise the cage by inserting blocks under the corners so that the chicks can come and go freely, but the big birds cannot get into it. After another week or two they're usually well integrated with the flock.
I brood my newborn chicks for three days inside with a heat plate and then transfer them and the heat plate to a bottomless cage on the floor of the coop (not under the roosts so that they don't get soiled as the adult birds sleep). Once the chicks are about two or three weeks old, moving about with agility, I raise the cage by inserting blocks under the corners so that the chicks can come and go freely, but the big birds cannot get into it. After another week or two they're usually well integrated with the flock.