Thanks for this, 21hens, very clear-cut!
Follow-up question, now that our chicks are 4 weeks old and we're starting to prepare for their transition...
A dozen hens is what we're aiming for, and it will be easy to expand their pen to make that work, and more (we will likely double the pen size). But at the moment we have 24 6-week olds, and hope to keep them until they are ~12 weeks old before harvesting roos (or having a second coop built). We also don't yet know their genders.
Do they need the same size coop and run as adults when they are 6-12 weeks old?
Right now they are in a 4'x12' run in our greenhouse, with a brooder plate and hiding box and roosting branch. I guess we could keep 3-4 roos in there beyond six weeks if we add a roost box to their area? Then we'd have 20-21 teenagers in the big girl coop from the ages of 6-12 weeks.
Will this work, or do we really need to build/improvise another coop solution in the next 2 weeks? We want another coop eventually, so it wouldn't be a waste, but we're in the middle of house build and would rather put that work off until spring...
I know, I know, we made an impulsive purchase when we weren't really ready for it, after having this great coop fall into our lap! We went a little nuts. And the kiddos are so great, of course. When we had backyard chickens we raised 25 from chick and shared them with other backyard chicken enthusiasts by the time they were big enough to move out.
Actually, that might be the best option -- to re-home chickens that won't fit in our coop. We are in a rural area and lots of folks have small family farms nearby.
Anyway, the main question is... is a 12-adult coop & run big enough for 20-24 12-week-olds?
Short answer is maybe.
Luckily the young get along better than those of breeding age (20 weeks or so depending on breeds).
Long answer is it all depends on how many males you ended up with and their individual temperaments. It can get really complicated really quickly.
Being in New Mexico you might be able to make a hoop run to house some if needed.
https://www.backyardchickens.com/threadloom/search?query=Hoop coop&tab=620