I'm not sure where you're located or how your building site is situated so this may not matter to you...
Being in south Alabama, I would extend the overhangs a bit. On the west side I would extend the overhang by close to 4 feet...storms normally come out of the southwest so it would help keep rain out of any open window on that side but most importantly would shade the west wall during the HOT hours of summer days...in the winter it would allow the sun to peek under the overhang and warm the side of the building. On the south I would extend the overhang out for another foot...this one would be more for the heat factor than for rain, though I may make a removable piece for the summertime that will extend the overhang a bit.
I happened upon an online calculator the other day that helps figuring overhangs for solar shading/gain. You might want to check it out, here's the link:
https://www.backyardchickens.com/forum/viewtopic.php?id=333328
Another thing that I would try to do is raise the coop up higher than one block high. 18"-24" would be good to give the chickens a good place to find shade, rain cover, build dust baths, etc.,. A coop floor low to the ground will invite unwanted critters, mostly rats, to set up housekeeping there.
This plan has always appealed to me for it's basic, functional design. I took am figuring on a removable poop board...whether proof it and predatorproof it and your set. The only problem with it is that the poop board is under the drip line of roof. When it is raining it's going to be somewhat problematical to access the board. I've seen lots of externally accessed nestboxes be placed in the same location...and wonder about the foresight in regards to rain draining off the roof onto the flock owner. Just something to think about.
Best wishes on your project!!! Keep us posted on the progress (with lots of pictures from the foundation up!
).
Ed