Delay in possession of flat by builder what action can I take

I have purchased a 1bhk in asangoan west in 2013. the possesion date on agrrement copy was sept-2015. 95% of the payment is paid to the builder but still the work of building is not completed. Now the builder is saying he doesnt have enough funds to complete the building and he would be require more 6 months to complete the possesion ( i.e:- dec2016). i want my money back with interest on it from the the builder, can you help me out regarding how ans were to file the case and how much time and money will be require to solve out the case?