Hello,
If there is a specific clause in the agreement that the premises would be leased out for 3 years by the builder you can send a legal notice to him for specific performance.
Since he has already got a lessee for you in a way his responsibility is over.It is not his responsibility as the lessee discontinued after six months.
What you should have done was to get the lessee get you a substitute or compensate you for premature termination of the lease.
Why don't you find a lessee by advertisement or agents?