Want to cancel my flat booking after 9 months of booking

I have booked a 1 BHK apartment in Ahmedabad. At the time of booking my personal loan was going on so I convinced my builder that I will not be able to get home loan untill and unless I'll close my personal loan which was supposed to end in just 6 months. By then I have committed him that I'll pay 3,70,000 at the time of booking and Rs. 10,000 every month from my salary by the time I'll close my personal loan is closed. The total deal value including registration/stamp duty/maintenance etc was Rs. 21,50,000 So by now I have paid him 4,60,000 in 9 months. He also was agreed on these conditions. There I have two concerns: 1) At the time of booking the builder committed me that I'll get the flat possession by Dec. 2015 but as of now only plastering is going on so it may take a min. of 8-9 months more min based on his speed of construction that I have observed in last 9 months. 2) Now due instability in my job, I'm planning to shift to Hyderabad. And I may not be here in Ahmedabad after even 4-5 months. a) I have not even applied for home loan yet. b) As of now there is no legal documentation is done with the builder. The documents I have are: 1) allotment letter, 2) receipt of Rs. 3,70,000 (cheque transaction), 3) One diary in which he supposed to write my Rs. 10,000 (cash) instalment every month and sign. I want to cancel my booking. What negotiation I should do with the builder please suggest.