Transfer of property when owner alive

Hi,

I have a commercial property (Shop) in Delhi that is in my Grandfathers name. My Grandfather is in good health but wants to transfer the property in my name. The Builder of the shop says they require a legal proof stating the transfer so that they can re-issue new property documents in my name. I wanted to understand what could constitute of legal documents for property transfer.I gather the following:-

1 - Gift Deep - Best option but this would require me to pay stamp duty charges which are steep in Delhi.

2 - Will - I have been told that this cannot be used as the will can be changed / revoked and should only be an option when the person transferring is not alive.

Is there any other option which I could use? 

Could a transfer deed could be used for this purpose?

Thanks!