[15] In the light of these two dates, the respondents cannot be permitted to levy extension fee by calculating the permissible construction period of four years from the date of “issuance of allotment letter/delivery of possession”. In other words, mere delivery of possession was meaningless for the petitioner-Society as it could have not commence the construction unless 'zoning plan' was issued and building plans were sanctioned. To say it differently, the permissible period of four years to raise the construction will have to be counted after 06.08.2008 only, i.e., the date when building-plans were sanctioned, say 01.09.2008 onwards. The construction cannot be started mechanically. Some breathing time has to be given for making necessary arrangements. Applying the principles of reasonableness, we are satisfied that the permissible period of four years to raise construction, in the case in hand, should be taken to have commenced w.e.f. 01.01.2009. In this manner, the petitioner-Society was required to raise construction on or before 31.12.2012. The extension fee/non-construction charges thus are leviable on it w.e.f. 01.01.2013. Further, the non-construction charges will have to be calculated as per the