OP, if you can be outdoors in shirtsleeves yesterday, then you are among those who can probably get away with less square footage. In Canada, one of our finest coop people on here won't keep them at less than 15 sq ft in the coop (not the run, and no that's not a typo) but hers stay indoors for days on end in the winter, probably weeks on end. In warmer climates, coops need to allow for plenty of breeze, and shade is a big plus. You might consider making some large areas of walls out of hardware cloth with wood awnings so you can let plenty of breeze in when warm weather shows up. Apparently we are colder than you as I wore a warm jacket yesterday and have had frozen solid waterers every morning for several days, but my coop has several sq ft open to the air on all 4 sides for plenty of summer breeze. My coop is not in a shady spot and they will go in during the heat of the day in summer just for the shade, unless I'm letting them free range, when they go to the woods. Chickens have a whole lot of cold tolerance but can actually die, are at least stressed enough to slow down laying, in heat, especially over 100 degrees F. Another thought is, in a good sized coop like that, the 4 sq ft is not nearly as critical as it is in a tiny coop. You will have some happy chickens!