JOE:
I dislike being asked for a "cost to cure", for several reasons.
First, I feel like I'm being asked to do someone else's job for them.
Second (I agree with you) I am not an expert in every field and am only there to observe and report, not to fix/repair the problem.
Third, must we ALSO keep a file on all of the current costs of housing materials? How many appraisers know the current costs "per square" of the ten or more grades of roofing shingles, as well as the cost per square to install?? Do you recommend a "re roof" (over existing) or "rip and roof" (totally remove all existing roofing material to deck). By the way, before you recommend either method, you have to be able to determine how many roof layers are currently on the home, and know the building code for number of layers allowed !!!!!!
Finally, what if your estimate is wrong ??? If you are really low in your estimate, does the lender or the borrower have a right to sue you someday?
You are right to be concerned and upset. My best recommendation is exactly what you said-----write the lender a letter telling them that you are a licensed appraiser, and can answer any appraisal question. Construction questions should be answered by a licensed contractor.