Answer:
ask the buyer if they would like to make an offer taking the age of the roof into account
Step-by-step explanation:
Based on the information provided within the question it can be said that the best thing that Bob can do is to ask the buyer if they would like to make an offer taking the age of the roof into account. Therefore if the buyer accepts the condition then the asking price will be adjusted to reflect the condition of the roof, meaning the buyer will lower the price.