In my opinion that would make a wonderful coop. I'm sure many folks here would just love to have something like that available to us.
I don't think insulation would be necessary, especially in GA.
I have a suggestion for the roof . . . don't go to the trouble of a shingled wood roof like you have now. Use framing lumber and plywood for the sides to build a flat sloped roof with either metal or translucent acrylic roofing. A 3"-in-12" pitch should be plenty of pitch to shed the rain (maybe even a 2"-in-12" pitch would be OK). The three vertical sides (one rectangle in the front and two triangle sides) would provide lots of flat space for ventilation openings. Slope the roof away from the door side of the coop to reduce the need for a gutter to reduce a muddy entrance. Include as much overhang as possible all around. This will aid in keeping the conc. block walls a little dryer at the bottom where mold and mildew likes to grow on block. Overhang will also keep the wooden sides above the block dryer, too.
I would also consider putting the little pop door in the existing people door. This would eliminate the need to chop a hole in the conc. block. You could permanently attach a small sloped ramp on the outside of the big door that would swing with the big door when you open it.
I don't think insulation would be necessary, especially in GA.
I have a suggestion for the roof . . . don't go to the trouble of a shingled wood roof like you have now. Use framing lumber and plywood for the sides to build a flat sloped roof with either metal or translucent acrylic roofing. A 3"-in-12" pitch should be plenty of pitch to shed the rain (maybe even a 2"-in-12" pitch would be OK). The three vertical sides (one rectangle in the front and two triangle sides) would provide lots of flat space for ventilation openings. Slope the roof away from the door side of the coop to reduce the need for a gutter to reduce a muddy entrance. Include as much overhang as possible all around. This will aid in keeping the conc. block walls a little dryer at the bottom where mold and mildew likes to grow on block. Overhang will also keep the wooden sides above the block dryer, too.
I would also consider putting the little pop door in the existing people door. This would eliminate the need to chop a hole in the conc. block. You could permanently attach a small sloped ramp on the outside of the big door that would swing with the big door when you open it.