How can I determine fair market value of a roof before and after damage from a federally declared major disaster?

It depends. A realtor may be helpful. Essentially, you determine the fair market value (FMV) before the disaster and then then subtract the cost of the roof replacement from the FMV. This would be one way to arrive at a FMV after the casualty.

The actual loss based on the cost of the repairs is $3,000. Since this was below your deductible, then the full $3,000 will be used on your less the $500 deduction without using itemized deductions, 

• If you have a qualified disaster loss you may elect to deduct the loss without itemizing your deductions. Your net casualty loss doesn't need to exceed 10% of your adjusted gross income to qualify for the deduction, but you would reduce each casualty loss by $500 after any salvage value and any other reimbursement. For more information, see the Instructions for Schedule A (Form 1040) 
  • IRS Topic 515
  • What if I have property that was lost or damaged (casualty loss)? Click the link 'Enter your qualified casualty loss'

Note: Intuit is currently waiting on guidance from several states on whether the state will conform to the Disaster Relief Act of 2023. As guidance is issued, Form 4864 for the states will be updated and made available.

@rebeccaerickson220

[Edited: 03/08/2024 | 2:34 PM PST]