When any new building is erected or when any building is rebuilt or enlarged or when any building which has been vacant is re-occupied, the person primarily liable for the property taxes assessed on the building shall give notice thereof in writing to the Commissioner within fifteen days from the date of its completion or occupation whichever first occurs, or as the case may be, from the date of its enlargement or re-occupation; and property taxes shall be assessable on the building from the said date.