The 2017 tax legislation changed the rules on the rehabilitation credit for historic building owners.
Form 3468 is the proper form to claim the credit.
- You get 20% of the qualifying costs for rehabilitating the building
- The cost of buying the structure is not included in the credit
- The 20% credit is amortized over five (5) years from the year the building was first put into service.
- Pre 1936 building 10% credit is eliminated. Transition rule now applies
- Transition rule: applies to pre 1936 buildings and a certified historic structure. Prior law can be used if the taxpayer owned or leased the building on January 1, 2018 and continues to own or lease after that date. Also, the 24-60 month period selected for the substantial rehabilitation test begins by June 30, 2018.
For a list of what constitutes a qualifying cost for the 20% credit see the link here. https://www.nps.gov/tps/tax-incentives/before-apply/qualified-expenses.htm
See also IRC section 47 for additional information on this topic.