Formerly my pup nursery until they were 3 weeks old was a 10 X 20 shed on a slab open on two sides (welded wire on open sides). After then they would be put in a 1/8th acre pen with trees for shade with gate being left open most of the time. Predator concern caused me to delay the transfer to 4 weeks.
In extreme heat while in the nursery I installed a cheap a/c which was a good investment. It was not efficient because of the open nature of the shed but it did cool it to the extent that the pups and mom were comfy.
Once in the regular pup pen heat wasn't a problem because they and mom could dig into cool shaded ground.