Please ensure that the following precuations are taken:

1) Ensure that the builder has a clear title on the property. This can be validated by asking for a title sertificate on the property from a authorised government solicitor or by asking the builder if he has pre sanction for home loans from a reputed bank

2) Ensure that the Agreement for Sale is not in conflict with the existing local regulations by showing the draft to your solicitor

3) Look for building plan approvals before booking any property. Copies of the same need to be provided by the builder to you as per Law. Ensure that the flat that you are purchasing has the correct buildup area as mentioned in the approved plans

4) Ensure that you get reciepts for all payments made to the builder in case of part payments based on stages of completion.

5) Ensure that the Agreement for Sale clearly mentions a completion date for hand over of the property to you.

6) At the time of taking possession, actually measure the size of each room  to ensure that the area mentioned in the agreement is what you get.