I have just about made it through the danger stages of outdoor brooding/cooping.
Look up Horizon Structures for their 4 x 6 foot Amish looking coop, that is what I have to brood/coop.
I lost one chick to, most likely, cooking to death one afternoon, and I have one in the hospital box cause she got trapped for two days before I found her.
You will need to have someone at home for at least the first 3 weeks to monitor the temps or you will kill some chickens.
I live in Florida, so that's a obvious heat problem. You are in Tennessee and your afternoons are going to get real hot real fast, faster than those little chicks, which I suppose you are getting day olds, are going to be able to handle.
You need an area, where the brooder is going to be placed, that is at a relatively stable temperature, plus or minus 10 degrees, like 60-80 degrees.
Then the brooder can function as it was meant to function, as a moderately effective temperature adjuster.
Remember this is of the utmost importance, your chicks need to get out of the heat as much as they need to be in the heat at times. If your shed stays at 90 degrees, where does the chick go to take a cool breath, even just for some relief from 90 degrees to 80 degrees for 2 minutes, nowhere. Over 100 degrees for a short time (2-3 hours) will damage or kill most baby chicks.
When a chick is so young things change very fast and their environment needs to be adjusted just as quickly, but they do that naturally when a hen is raising them, now you are the hen.
After the first couple of weeks they will be able to tolerate more extremes in temperatures, but still need close attention to those afternoon temps.
I employed my wife, after her lengthy protest, to check the thermometers almost hourly throughout the afternoons, it was a great help to me.
My only solution came when I just decided to open the chicken coop door in the morning and let them go outside, in an enclosed run, to cool off. Some were not able to navigate the ramp yet (at 8 days old) so I tossed them outside and now they are doing fine at 5 weeks old. But they are outside, under the 2-foot-off-the-ground, raised coop.
My wife was a great help for those first two weeks, and once the neighbors needed to open some vents while we were out on afternoon too long.
Remember baby chicks are babies. Babies need constant care or they will die.