The provisions of this Act shall apply to every apartment in a multi-storeyed building which was constructed mainly for residential or commercial or such other purposes as may be prescribed, by--
(a) any group housing co-operative society; or
(b) any other person or authority,
before or after the commencement of this Act and on a free hold land, or a lease hold land, if the lease for such land is for a period of thirty years or more:
Provided that, where a building constructed, whether before or after the commencement of this Act, on any land contains only two or three apartments, the owner of such building may, by a declaration duly executed and registered under the provisions of the Registration Act, 1908 (16 of 1908), indicate his intention to make the provisions of this Act applicable to such building, and on such declaration being made, such owner shall execute and register a Deed of Apartment in accordance with the provisions of this Act, as if such owner were the promoter in relation to such building.