There are plenty of great responses on here in regards to high heat.

I live in Kern County, CA... I'd like to say it's also as hot as the surface of the sun. Summer outside temps usually hover at 100-110 during the summer. I have an outdoor thermometer in their coop to monitor conditions closely, and it usually runs about a degree or two higher then outside temps. Chickens panting is pretty typical for me, but several things I do to try and help... provide a clean and cool drinking water source daily (something they can't soil), provide cool water in bowls of some sort they can stand in or on the edge of (these will get filthy, so be prepared to clean daily or several times daily if you can). I have a mister in my run I turn on for days over 105. This gives cooler dirt for them to lay in. If not a mister all day, then I will hose down certain shady areas in their run for the same purpose. They get cooler snacks such as frozen watermelon, cold grapes. I have a small fan inside the coop pointed toward the nesting box for any layers. The heat usually zaps my egg production, and I don't blame the ladies, I don't want to do anything either when it's 105 outside. You can try frozen water bottles in the nesting boxes to help the girls out. I also have a fan in the run to give them some air circulotation on those days that are stiflingly still. My humidity is typically low, I think it averages between 10-20% (yes, I also have a humidity meter in my run), so the mister doesn't really have a big impact on humidity. It's one of those S shaped ones that sits on the ground. And of course, a somewhat heat tolerant bird is a must.
If all else fails and they give me the sad eye, I open the back garage door and let them chill in my garage for the day (which is ducted with the house swamp cooler)... although it leaves a very LARGE mess in my garage. Then they get booted back out after the heat of the day. But I do have to work, so they don't get this luxury all the time.