You may have difficulty determining the fair market value. If you owned the sites less than 1 year, your deduction value is the FMV on the date the previous owners died. If you have owned them more than 1 year, the donation value is the FMV at time of donation. Keep records of how you determined the value. If the value is more than $5000, you need an appraisal, and you need to file with your tax return, a copy of form 8283 that is signed by the appraiser and by an authorized representative of the charity. See publication 526.
https://www.irs.gov/pub/irs-pdf/p526.pdf
