First of all...plan for more space, because you are most likely going to want MORE the following year
I was fortunate enough to have an old shed/garage to start with...so I had way more room than was needed (to start with...)
we levled out the dirt floor and laid down heavy plastic, then threw some gravel on top...built a floor with rough lumber we had cut from a tree that came down during a storm the winter before. ]
Built up and insulated with fiber board on the south side, what was originally the two garage doors...put in one screened window in on the south side, "people" door with window and another window on the west side, chicken door, to outside enclosure, and another "people" door with window on the north side...and with a light in the winter, had eggs everyday!
Now that's without any REAL insulation, they did just fine...however there were some mornings with frozen waterers and once or twice I had found a frozen egg. So I did suspend a space heater from the ceiling with a metal hook, it hung about 3 ft off the floor...it had one of those safety settings that i would shut off if tipped over, but I still didn't want the risk so I set it at the lowest setting and hung it up so the girls couldn't mess with it.
Did the whole "deep litter" method, which my garden thanks me for....
That was last year and my first year to have chickens....this year I just had to get more....and with some more free and found materials, I've now got a giant, thermal pane picture window in on the south side of the coop, just moved the little sreened one I had over a few feet...was able to reshingle, vent and insulate the roof....I'm thinking with all the remodeling and the sweet redecorating, my new and old girls will be cozy, warm, and happily laying all winter long again
I've got a mixed flock of about 35 with 2 roosters....I have a nesting box that an "old" friend of ours insisted on building, and he's 91, so I wasn't about to disagree, and it has 10 nests in it, more than I need, but nice to have in case I want to and will most likely, get more chickens.
I was also able to build an innner enclosure, that was big enough to fit the brooder box that our old friend built for us, and to keep the babies away from the older hens this last spring...some 2x4s framed off and some chicken wire, and another old, free door.
I guess my main advice is to plan BIGGER...than what you think you'll need, try to "find" as many building materials as you can, and then find or buy a little extra, especially for chicken wire and fencing, because there will most likely be someplace, you don't want them getting into or out of
