While they are in the brooder, its recommended at least 6 square inches each. If they are bantams, a little less. Out in the coop you want a MINIMUM of 2 square feet per bird in the coop on floor space, then a foot each roost space. More room is best
I picked up the book "Raising Chickens for Dummies" cause this is my first time with chicks. Tons of awesome info...you will find great advice here too.