A modular assembly structured to assume either a shipping container configuration or a building unit configuration including a frame comprising a plurality of support members and defining both a part of the building unit configuration and shipping unit configuration. A plurality of frame panels are movably connected to the frame and disposable in either a closed position or an opened position so as to respectively and at least partially define either the shipping unit configuration or the building unit configuration. The plurality of unit panels are movably connected to the frame and disposable outwardly therefrom to collectively define end wall portions and ceiling portions of the building unit configuration wherein the unit panels may be stored within the interior of the frame. An erection assembly is selectively disposable in an assembled position exteriorly of the frame and supported thereon so as to facilitate the assembly of at least some of the frame panels and/or unit panels.