THere was a long thread here last year (you could probably find it with 'search' and a bit of reading) on this subject, entitled I believe "what would you do differently" or some such thing.
Virtually everybody listed as their #1 mistake, "should have built much bigger coop" LOL
My chickens are currently living in a bldg I didn't build myself, just retrofitted for chickens (previous owners of this place built it as a dog boarding/breeding kennel). On the whole I like it a lot, but there is one BIG thing I'd change if I easily could, which is:
I would
kill to have a people door leading directly from coop (pen) into run. As it is, if I have to shoo chickens inside, I have to walk outside and around the end of the building, shoo chickens in, then race out of the run (not neglecting to latch door), back around the end of the building, in the building door and down the aisle and into the pen, and slam the popdoor shut, by which time of course half the chickens have wandered back outside again
I've worked out a few things to slightly streamline this, but MAN OH MAN do I wish I could just walk from the run directly into the coop.
Highly recommend for anyone doing coop design for next spring...
Pat