1) You are entitled to have your lawyer( it is your fundamental right under Constitution) for legal vetting of the title deeds and also at the time of registration. Article 21, 22(1), 39A are fundamental rights of citizens and right to legal aid is enshrined in these articles.
2) Builder cannot enforce upon you to consult with a lawyer of his choice.
3) It looks like a ploy by the builder to deviate from his deliverable's(handing over possession, registration) and instead divert you towards non -core issues
4) Please issue written Notice / mail to builder that
a) He cannot refrain you from engaging the services of a lawyer of your choice and
b) The builder shall be solely responsible for any costs if he chooses to arbitrarily cancel the agreement and
c) You are entitled to claim 100% of monies paid by you along with 18% interest should the builder unilaterally cancel the agreement.
d) Direct the builder to complete his part of contract (registration and possession etc) as per time lines agreed.