(1) The Commissioner may at any time during the erection of any building or execution of any work or at any time ¹ [after the completion thereof, by a written notice of not less than seven days], specify any matter in respect of which such erection or execution is without or contrary to the sanction referred to in section 336 or is in contravention of any condition of such sanction or any of the provisions of this Act or any bye-laws made thereunder and require the person who give the notice under section 333 or section 334 or the owner of such building or work either—
         (a) to make such alterations as may be specified in the said notice with the object of bringing the building or work in conformity with the said sanction, condition or provisions, or
         (b) to show cause why such alterations should not be made, within a period stated in the notice.
     (2) If the person or the owner does not show cause as aforesaid, he shall be bound to make the alterations specified in the notice.
     (3) If the person or the owner shows cause as aforesaid, the Commissioner shall by an order either cancel the notice issued under sub-section (1) or confirm the same subject to such modifications as he thinks fit.