This research discusses the proof of building ownership based on the principle of horizontal separation. Is it possible for the Government of Indonesia to create a special agency for building certification without land rights? The Indonesian agrarian law adheres to the principle of horizontal separation, where a party can construct a building on land owned by another. To be able to protect their rights, the owner of the building requires proof of ownership that is separate from the proof of land ownership on which the building stands. As building is classified as immovable property namely object adhered to the soil, a written proof (certificate) is required as proof of ownership. This is normative descriptive research. The results show that the Indonesian government can establish a special agency for building certification without land rights, such as the National Land Agency (NLA) to ensure that buildings without land rights can possess legal certainty which enables them to be used as collateral.