If you’re on a tight budget, think about using shipping palettes. Our TSC gives them away. Some places sell them. Stop and ask when you see a pile of them behind a business. Look on Craig’s list... you may find some. If you put them together securely you can always upgrade the siding to make it pretty.
If you post more about your situation, your goals, your general location (for weather considerations), then folks can offer more useful advice.
Get a copy of Storey's Guide to Raising Chickens, 4th Edition: Breed Selection, Facilities, Feeding, Health Care, Managing Layers & Meat Birds
https://www.amazon.com/dp/1612129307/?tag=backy-20
Totally worth your time to read that one.