My basement flooded, where i had to spend more than 10K on cleanup/gutting, and then remodeling costs. How do i calculate the Fair Market Value before/after loss?

Here is how casualty losses work: Individuals are required to claim their casualty and theft losses as an itemized deduction on Form 1040, Schedule A Itemized Deductions. 

1. For property held by you for personal use, Subtracted any salvage value (zero for theft) and any insurance or other reimbursement from the loss amount.
2. Then, subtract $100 from each casualty or theft event that occurred during the year. 
3. Then, take that amount and subtract 10% of your adjusted gross income from that total to calculate your allowable casualty and theft losses for the year.
4. That's the amount that goes on your Schedule A Itemized Deductions.

If your property is personal-use property or is not completely destroyed, the amount of your casualty loss is the lesser of:

• The adjusted basis of your property, or
• The decrease in fair market value of your property as a result of the casualty

More details can be found at this link  http://www.irs.gov/taxtopics/tc515.html

That said, the amount would have to be pretty large for you to be able benefit.  Also, you must file Schedule A as I stated above.  But, if you want to give it a shot in the Casualty and Theft section of the software, it wouldn't hurt.

Clean-up

Cost of cleaning up or making repairs. The cost of repairing damaged property isn't part of a casualty loss. Neither is the cost of cleaning up after a casualty. But you can use the cost of cleaning up or of making repairs after a casualty as a measure of the decrease in FMV if you meet all the following conditions. The repairs are actually made. The repairs are necessary to bring the property back to its condition before the casualty. The amount spent for repairs isn't excessive. The repairs take care of the damage only. The value of the property after the repairs is not, due to the repairs, more than the value of the property before the casualty.