The size dimensions of your structure include its width, length, and height. The width is measured from the outside of one base rail to the outside of the next; therefore, the base rail is always 1’ shorter than the roof itself. Height is measured by the actual height of the legs on the outer walls. Keep in mind, there is no overhang included with A-frame horizontal or vertical roofs, meaning the actual length of the unit is the length of the base rail.