An appraisal is an estimate of value of a property by an independent, licensed appraiser. Your lender will need an appraisal in order to approve your loan.
If an appraiser is concerned about a structural component of the home (like the roof) the appraiser may call for it to be repaired in order for the value to be valid. That being said, an appraisal is not a home inspection and should not be considered so by the buyer. The appraiser’s main function is to simply verify the value of the home for the bank. The appraisal is paid for by the buyer as part of their loan costs but works for the lender.