A home inspection flags major issues, but it won't tell you how much longer the roof or HVAC system will last. If the roof is 15 years old and has a 20-year lifespan, you could be facing a $10,000–$15,000 replacement in just five years. Ask the seller for receipts on recent replacements and repairs, and get a sense of the home's true age. Budget for a roof replacement, furnace repair, or foundation work in your financial plan—these surprises derail countless new homeowners.