Words used in the present tense include the future; the singular number includes the plural and the plural number includes the singular; the word "lot" includes the words "plot" and "parcel"; the word "structure" includes the word "building"; the term "occupied" or "used" as applied to any given building or land shall be construed to include "arranged," "designed," "constructed," "altered," "converted," "rented," "leased" or "intended to be used or occupied"; the words "shall" and "must" are intended to be mandatory and not optional.