If you get big breed hens, you could take out one of the dividers, so there's a box 20" wide. An easy fix!
Your pullets and hens will show their preferences anyway.
Mary
It's nice to use untreated, but here, if it touches ground, it's treated. Our coop is on an old building foundation, so old broken concrete, with a rat barrier, and rubber stall mats on top. There's no crawling under the coop here!!!
As @aart said, use good grade vinyl so it holds up better.
Mary
I would add something to that plywood floor.
Critters can chew through it, BTW.
At least several coats of sealer, deck paint, or a scrap of vinyl flooring.
Wide roof overhangs are very helpful too.
Mary
Nice! You can raise them right in that coop, at least after the first week or so. Shipping is hard, so I like mine in my garage brooder for a week or so. Actually, mine stay in the garage for a bit over two weeks, so their Marek's vaccine has time to work.
Assortments are fun! Especially...