Definition of transfer

To avail the exemption u/s 54 the reinvestment in new house property should be within the time frame of 1 year before or 2 years after the date of transfer (sale).

In your case date of possesion (june 2012) would be considered date of purchase of new house property. Though there are cases where the court has held the date of allotment as date of acquisition but that is the case where the buyer has paid all the money at the time of allotment. Since you paid the amount to the builders over a period of 3 years and not at once, the date of possession is the date of acquisition.

Thus...benefit of Section 54 will be available as possession of the new house property is within one year before sale of  house. 

However you will get exemption u/s 54 in AY 2013-14 and not in AY 2014-15. This is because sale of house was in Feb 2013 i.e AY 2013-14. Since Capital Gains arising on the transfer will be charged in AY 2013-14 the benefit u/s 54 can be availed in the corresponding year only and not in later years.