School project? This is a very good question not easily answered. Lets say you live in the state of Alaska verses the state of Texas. Climates are entirely different and so are the crops that are available. Common feed for chickens is anything they might forage for and consume. That includes bugs, weeds, grass, grains, berries, and their diet is unlimited. If you put it in their dish and they eat it, its common! Commercially, manufacturers have put together what seems to be all the required supplements and nutrients to raise healthy chickens. Across the vast expanse of the United States, farm agriculturalists grow many of the products packaged and sold to chicken owners. Depending on where you live, the needs for your chickens may differ and the product you purchase has all the needs regardless of where you might live. Mostly, depending on the chicken breed you are raising.
A farmer may purchase his feed from a local grain maker or the local feed store. They should both provide the ingredients required for raising healthy chickens. It is up to us the consumer to read the label as to what our chickens are eating! Truthfully, the diet of chickens is anything but common! Yet, we have common types of processed commercial feeds and brands formulated for use. My gosh! The names and different types nation wide are way too many to put into words. The one thing I will tell you that most people have in common is the "cost" and not always the brand label.
Good luck with your project and share your feedback! Good luck.