Temporary permits may be authorized by the Planning Board for a period not to exceed six months for nonconforming uses incidental to housing and construction projects, including such structures and uses as a shed for the storage of building supplies and machinery and a real estate office located on the tract offered for sale, provided that such permits shall be issued only upon agreement by the owner to remove the structure or structures upon expiration of the permit. A trailer may be used for such office purposes but not for housing or sleeping. Such permits may be renewed for a further period of six months upon good cause shown.