The Chief Administrator may authorise any person, after giving twenty-four hour’s notice to the occupier or, if there be no occupier, to the owner of any building or land, at any time between sunrise and sunset-
(a) to enter in and to survey, and to take levels or measurements of any building or land, or
(b) to enter into any building or on any land for the purpose of examining works under construction or of' ascertaining the course of sewers or drains, or
(c) to enter into any building or on any land for the purpose of ascertaining whether any building is being, or has been, erected or re-erected without sanction or in contravention of any sanction given under this Act or the rules made thereunder, and to take such measurements and do any other such acts, as map be necessary for such purpose.