This “barn spider” is probably Neoscona crucifera
, also called Hentz’s orbweaver and spotted orb weaver. It’s a widespread species that commonly builds its webs in woods and on the eaves of barns and other structures (including houses). The female takes down her web each morning, hides in cracks and corners during the day (as shown in this picture), and spins a new large, round web at dusk. This individual built her web next to a dusk-to-dawn porch light each night for several weeks one late summer, taking advantage of the host of flying insects attracted to the light.