The Planning Board shall have the power to grant a temporary building permit for a period not to exceed one year for a nonconforming building, structure or use incidental to a building or other construction project, including such uses as the storage of building supplies and machinery and a real estate office located on a tract of land where individual properties are being offered for sale, provided that such temporary permit shall be issued only upon written agreement by the owner or his agent to remove such building or structure upon expiration of such permit, and further provided that such permit shall be subject to such reasonable conditions as said Board shall determine to be necessary to protect the public health, safety and welfare. Such permit may be renewed annually, at the discretion of the Board, over a period not to exceed three years.