www.backyardchickens.com

All the rage!  We have cedar to help you build more than a simple cage.

The general rule is 4 square feet of inside space and 10 square feet of run space per standard sized bird, half that for bantams. I've seen some people give their birds 2 square feet per bird inside the coop, but those birds are almost never in the coop. Your coop and run sound about right for 4 hens, though if it snows a lot in your area (I don't know what Utah is like) you may want to build bigger as the hens will be stuck inside a lot. The general rule for nest boxes is 1 for every 3-4 hens in the coop and for roosts 8-12 inches per standard bird and half that for bantams. You already got 8 chicks so if you feel your coop isn't big enough, make a second (you can connect them through the run) or add on to your current one. 

 enjoy your chicken adventure