Suggestion regarding "Flat possession delayed"

Hello, We had booked a property whose construction has been delayed for quite some time now and i am seeking some guidance in this issue. Brief about our property: The property is located in Goregaon East (Western suburb of Mumbai) and was purchased back in December 2009 @8000 sqft. The construction is currently at a standstill and has been for a while. Different reasons have been cited at different times for the cause of delay, the current one being "MOEF clearance pending". Owing to the frustration of the buyers, last month i.e March 2015, the builder had come up with couple options for the buyers: 1) Buyback option - Buyback @ 13% simple interest. 2) Extra Amount option - Pay certain amount to stay with the flat option Question/Suggestion required: 1) My family has lost patience and trust in the builder and are seeking to opt out with a reasonable compensation. What do you think would be a reasonable compensation in this regards? (Note, that the current rate in the area averages to about 18000 psft.) 2) What is the approach a buyer should take in cases like these in order to get reasonably compensated? Thanks!!