I am an US citizen and an OCI card holder. I recently purchased property in Inida . The Property is still under construction and not expected to finish till next year although I paid for it this year (taking a loan from my 401k) . Where should I report this investment if it needs to be reported ?

No, you do not report the investment. You may be required to file Form TD F 90-22.1 to report your bank account and financial account info.