The short answer
A sanctioned building plan before starting, and an occupancy or completion certificate once the house is finished.
You apply to the local municipal or panchayat authority with a site plan, ownership documents and drawings prepared by a registered architect or engineer. Work should start only after the plan is sanctioned, and deviations from the sanctioned plan should be regularised.
On completion, an occupancy or completion certificate confirms the building matches the approved drawings. Missing approvals make utility connections, loans and resale harder, so keep every sanctioned drawing and receipt.
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