1) in the event cheque of Rs 6.75 lakhs get dishonored you can issue legal notice under section 138 NI within period of 30 days from date of intimation of dishonor
2) in case builder fails to make payment within period of 15 days of receipt of notice you can file complaint before Magistrate under section 138 NI
3) you can also file summary suit for recovery of amount of Rs 6.75 lakhs with interest