I just built my coop this past month. (Should've been week, but it took forever).  I have a large window for ventilation, insulated ceiling, double layered flooring, and an infrared heat bulb.  I also have a heated waterer w/ thermostat control for winter.  I plan to surround outside(bottom) w/ bales of hay for added wind protection.  Maine winters are tough, but I think we'll make it just fine.  As for a/c, we don't get enough "heat" in Maine to worry about them getting too warm.  I did put a childrens plastic swimming pool in the run in case they need a bath or want to cool off ...lol...