Here in Colorado, when it comes to the big issues, the inspector usually recommends that a professional is consulted.
For example, a roof that appears to be near or at its end of life - inspector would likely recommend a certification be obtained, which requires a licensed roofer to determine whether there is a certain number of years that can be expected before the roof fails. I've never seen a roof that could be certified if the inspector recommended it. In other words, if the roof looks questionable to the inspector, it turns out that the roof needs repair or replacement.
I always advise my buyers to require the seller to obtain this certification, at the seller's cost. If that's not possible, the buyer should get estimates for roof repair or replacement before the inspection period ends, in case they feel further negotiation is justified.
The same process is followed for the furnace, structural issues, etc.
You need a knowledgeable inspector who won't miss important issues, and who won't create mountains out of molehills. Your agent may have some to recommend, but you can also find them on your own. Ask them about certifications, experience, referrals, etc.