Delay in Possession of Flat by Builder

CASE SUMMARY: We made a booking with Imperia in their housing project 'Esfera' for a 1650 sqft 3 BHK apartment (D 1803) in December, 2011 At the time of booking we were committed possession by December, 2014 However, for more than 2 years no construction took place. Reason for delay was the lack complete approvals and permissions on Imperia's behalf. In this time, the initial proposal to build a 19 floor building was revised to build a 23 floor building and we were asked to pay an additional PLC amount of INR even though no such amount was mentioned in the buyer builder agreement. After several follow ups, and multiple visits to Imperia headquarters in Noida, the amount was removed from our payables The construction was initiated in February, 2014 (i.e. 10 months before the communicated date) clearly indicating that there was never an intent to meet the original commitment of possession in 2014 As on May 2016, the construction is at casting of 15th floor. The estimated possession date has often been revised At present Imperia is indicating that it will take another 1.5 years to complete construction taking the possession to mid December 2018, ie. atleast 4 years later than committed However, the pace of construction is still very slow and its seems unlikely that Imperia will be able to meet this deadline RELIEF as per my understanding: The delay in possession is a material hit to us financially and we would want a refund of the amount paid along with damages for the delay at their end. I want some guidance on the relief that I should demand for and how do I calculate the penalty amount.