My bua wants to gift my maa ₹15 lakh for buying an apartment soon. Should we prepare a gift deed? If yes, does it need to be registered and will there be stamp duty? What would the approximate cost be?

Yes, it is advisable to prepare a gift deed for the ₹15 lakh gift. The gift deed needs to be registered and stamp duty will be applicable. The stamp duty will vary depending on the state where the property is located, but it is usually around 1% of the value of the gift.