I spent way more than I thought I would buy trying to save on the first one. Bought wood I was told would work, I knew I shouldn't have listened. Then had to buy new more expensive to replace it. On the second coop, I made my plans and didn't listen to anyone else. I looked up coops online and read what people would have done differently to avoid mistakes. I love my new one. So much easier. ANd I can watch my chickens from the house if I want to.
We took inspiration from plenty of coops, but came up with something entirely our own. I seriously have never seen a coop like mine

We used some unusual materials, but they just worked. Like the posts... yeah, they're landscape timbers, because they're WAY cheaper than 4x4s The walls are fairly thin OSB, but we put felt paper over it and mounted fence pickets over that. It looks GREAT, it's sturdy and it was pretty cost effective.
I think I probably have $600-700 in the coop, rain barrel system and the 6 ft run.
I've had it for a year and I still gush about it haha. My husband just did a great job, turning my ideas into reality.
The only thing I learned is that it's never big enough. My initial plan was that the chickens would be contained in the coop. No free ranging, no additional run. HAHA. Right. First I made a little make-shift free range area, then it became bigger and more permanent, then they had the whole yard... until they started jumping the fence to the neighbors! Add a hawk attack to that and the 6ft tall run was born.

Love it none the less.
Coops evolve. They just do. You always find stuff to add.