This is my response to you:
1) What are the consequences if registry is not done on the date mentioned in the agreement?
Answer: The registry should happen on the 26th otherwise then the seller can take action against you. This is because you have violated the terms of the contract from your end therefore he can state that you are legally liable;
2) As a buyer what can i do to safeguard myself legally?
Answer: Therefore make sure you have made the balance payment otherwise he would initiate legal action. Also approach the registrar and do the registry;
3) can builder cancel this deal stating that registry was not done on time?
Answer: Yes he can cancel the deal;
This is my response to you:
1. If the building construction is not complete then why are your going ahead with the transaction?
2. Has the OC and CC come? Has he given a specific date?
3. If the construction is not complete and there seems to be no chance it will be, you may also back out from the transaction;
4. Make sure you don't have to forfeit any amount for the backing out from the transaction;
5. The sale looks suspicious therefore after verifying everything then only go ahead with the sale.