For an older home, you should ask the seller for a detailed Property Condition Disclosure. Ask how many years the first roof lasted. Ask when the second roof was installed. Do the same for the HVAC system. As you probably know, roofs and HVACs tend to be the most expensive upgrades to a home. Then hire a competent home inspector, someone who will spend several hours on his/her inspection. That report should give you a good roadmap to follow on maintenance and repair issues.