Look for visible signs of wear such as missing, curling, or cracked shingles, rust spots on metal panels, sagging areas, or persistent leaks after heavy rain. Inside the house, water stains on ceilings or in the attic, daylight showing through roof boards, or a musty smell can also indicate trouble. A professional inspection every year or two is the surest way to determine whether a targeted repair or a full replacement is the best solution.