@3KillerBs is in your general (in the most general of sense) area.
They can tell you much better what works for your general area, I feel.
You don't have to have a walk-in, sure.
I feel though that it is easier for me to take care of the run.
Also, unless you are in the wild mountains with oodles of snow and freezing winds, you might be able to get away with a minimal structure: Unless the temps dip into single digits here, I don't see that I will need much more than what I have now: a wire run with half the roof covered. They will probably need more food when it gets cold.
Look though the galleries, there are coops of every size and shape the good folks of BYC have built.
In terms of prefabs, you have to really be careful. most are much smaller than indicated.
I have one I don't think I could fit 2 bantams in. I am keeping it, in case I want to get more chicks. but so far, the playhouse is no more than a yard ornament. Maybe a hospital station, if needed. Prefabs are not designed by chicken owners, and it shows (I had to lay on the ground and reach far back to grab my chicks when I had them briefly outside while I cleaned their brooder.)