Yeah I have to admit that although I'd wanted chickens since I was young (to the point that my parents even took me to visit a cousin who had a flock, though all I was allowed to do was throw them some scratch) I never actually touched a live adult bird until about a month before we were planning to buy chicks. Didn't realize how big some birds got, because my only reference for "chicken" was a rotisserie bird from the market.
I did do my research but we still opted for a prefab (a much higher quality one than most) at first, with plans to upgrade if we liked keeping chickens. After 2 years we decided to grow the flock and replace the coop as well. Pretty striking what a 4 bird prefab (on right) looks like next to a 12 bird coop (on left) even though both have 4 sq ft of floor space (per bird):
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The prefab didn't go to waste - the top portion is still in the run as a brooder/isolation cage, the bump out on the right side still works as a rain shelter/feed area, and the remaining long wall is a compost sifter.