WOW -
One of my favorite topics, always has been a sore spot, especially with FHA appraisals.
First of all, I collect as much information regarding the roof as I can - it rains in Florida. I inspect it from the ground level, if necessary I get on a ladder. I ask the owner the age of the roof and what documentation they have, if any, to support the claim.
The typical fiberglass shingle roof in Florida last about 14 years, max. This is due to the pitch of many roofs and inadequate ventilation. If I determine the roof is 10 +/- years old I might say "The roof appears to be 10 +/- years old. No signs of active or previous leaks were observed on the interior; none were reported by the property owner. The roof is expected to provide weatherproof coverage for 2-6 years."
I let the lender know. That house falls apart from water damage 2-3-4 years after the appraisal it is not my problem. I will take pictures when active or previous leaks are observed - AND they go in the report. This is defensive appraising.
Regarding adjustments. A roof replacement costs about $5,000 for the typical Forida home. If your subject has a 10 +/- yo roof and the comparable has a new roof, obviously, you should be considering the difference in age in your overall condition adjustments.
FHA has specific guidelines on roof age, or more accurately, the length of time the roof is expected to provide weatherproof coverage. The minimum down-payment buyer has NO funds to replace a roof 1-2 years after they close on the home.
My comments are NOT specific to FHA appraisals. The house with the 10 +/- yo roof typically does NOT need roof replacement. You still need to protect yourself. And granted, some lenders would not want any comments about the 10 yo roof being made. They go in my reports - period. If the roof is 4-5 years old - I'll report that as well. Bet your backside the client knows with I think about the roof's condition. Like I said - it rains in FL.