Could you please help me to know if,
1. Builder can deduct 10% without a written agreement between 2 parties?
A registered sale agreement shall be the valid document for th terms and conditions therein to be complied properly by both the sides to enforce the terms and conditions through court.
In the absence of a proper sale agreement, the builder's claim appears to be exorbitant.
You may issue a legal notice and seek refund of the entire amount without any deduction except a minor amount towards the charges for this.
2. If he deducted 10% amount, how to handle this case or whom to approach?
Send a legal demand notice and then file a money recovery suit against him.
3. Since I broke FD and paid him, can I collect interest from him on paid amount?
The cancellation was in yor interest hence the claim for interest shall not be maintainable.
4. In requesting refund, I wrote emails (from my gmail account to his official server emails) to him to remind. Can these emails be used for legal case?
Yes, this can be treated as valid demand notice.
6. Legally, can builder deduct money saying that he lost clients because of my booking?
Waiting for your response.
In the absence of sale agreement this claim shall not hold good ground