Figuring out roof replacement cost by roof size is mostly about square footage, but it's never just that. A 1,500-square-foot roof might run you $7,500 for basic asphalt shingles, while a 3,000-square-foot home with steep pitches and multiple valleys can easily hit $20,000 or more. The size sets the baseline for materials and labor, but factors like your region, tear-off layers, and underlayment quality shift the final number. Contractors often quote per square (100 square feet), so before you… roof replacement cost by roof size 12