Resale of unregistered/under construction apartment

A. You need to collect NOC from the Builder in connection with the same.

B. You have to confirm with the builder regarding How much conveyance charge has fixed by the Builder?

C. You better wait till the completion of the construction and later, you can purchase the flat because of once construction completed that Apartment Association to be established, later society cannot charge more than Rs. 25,000/- charges towards the transfer fee. 

1. Execute and register a tripartite deed for conveying the title of the property between the developer, 1st buyer and you,

2. Pay the part amount through DD if the construction is not over and full amount if it is over at the time of registration when possession letter also should be collected.

You may follow the suggestions given by learned advocate Mr.Ganguly in this regard.  There is no problem in executing a tripartite agreement but you got to be careful on the payment matters.