What kind of certifications are required for a plane manufactured for personal use?
As Andy pointed out, this question is very broad (even if we're only talking about India). Your starting point should be the Directorate General of Civil Aviation (DGCA) because they can tell you definitively what would be involved in getting a "homebuilt" aircraft approved to fly under Indian law.

Information about this is available on the DGCA website and is broadly similar to the FAA's "Experimental: Amateur-Built" certification requirements:


The aircraft needs to be constructed in accordance with the DGCA's acceptable methods, techniques, and practices. Basically this means you can't use chewing gum as a structural fastener: The aircraft needs to be safe to fly.
The aircraft will be inspected by a DGCA representative prior to being allowed to fly.


  Note that the DGCA inspection is mainly looking for "obviously unsafe" conditions - they don't do a teardown inspection so if you used chewing gum as a structural fastener and subsequently that area is covered up by a wing skin the inspector won't know, but you will when the wing falls off on your test flight.

You will need the DGCA to issue you a Certificate of Airworthiness before you can fly the aircraft around - that certificate is contingent on completing required test flights at the airport where the aircraft is based/built.
You will need an appropriate pilot's license (and medical certificate if applicable) in order to fly the aircraft (this is also required to conduct  the Certificate of Airworthiness test flights mentioned previously).