A detached garage of not more than a two-car capacity, used solely by the persons living in the dwelling house, and a building for housing garden tools, provided that such garage or building is on the same lot as the dwelling house or on a lot contiguous thereto. No such accessory building shall be constructed upon a lot until the construction of the dwelling house has been commenced, nor shall an accessory building be used unless the dwelling house has been completed and put into use. No such accessory building shall exceed 450 square feet, and it will be a maximum height of not more than 16 feet to the peak of the roof.