Under RTI you can ask for the copy of approved building plan by the BBMP if the property comes under the jurisdiction of BBMP. The Bruhat Bengaluru Mahanagara Palike is the administrative body responsible for civic amenities and some infrastructural assets of the Greater Bangalore metropolitan area. The BBMP represents the third level of government (the Central Government and State Government being the first two levels). BBMP is run by a city council composed of elected representatives, called "corporators", one from each of the wards (localities) of the city. Hence, it is a Public Authority u/s 2(h) of RTI ACt, 2005 and hence, application can be made u/s 4 and 6 after payment of requisite fees.
Please refer: onlinerti.com/how-to-file-rti-online-for-karnataka for filing the RTI application for the same.