99% of my building is done in flip-flops and surf shorts (I hate cotton in humidity). Little hot in FL
I learned in the Marines to wear proper foot protection.
I learned building with flip-flops... when you drop a Tungsten bucking bar toward your foot... move like a Ninja!!!
I dont recommend flip-flops while building, but 2 years and I'm only down 2 or 3 toes.