Any proposed structure which will, due to an ordinance amendment, become nonconforming but for which a building permit has been lawfully granted prior to the effective date of a new ordinance taking effect, may be completed in accordance with the approved plans provided construction is started within 60 days of the effective date of the applicable ordinance, is not abandoned for a period of more than 120 days, and continues to completion within two years. Such structure and use shall thereafter be a legally nonconforming structure and use.