Give them till they're about four to five weeks old and you'll start to notice some differences. In alot of breeds, the roos do feather out slower, especially across their wing bows; what I call their shoulders. The cockerels combs will become larger and redder. They'll also have more wattle development than the pullets. As the tail feathers come in the cockerels tails will come to a definite point, while the pullets will remain a few fingers wide. They say that the legs of cockerels will be longer and thicker, but since I am raising a heavy breed, all of mine have pretty thick sturdy legs.