A building structure assembly comprises the following standardized interlocking components, which can be sized to suit any particular size of building required and ISO standard shipping containers, and includes at least one modular base structure, at least one modular base structure and at least one wall support in the form of a shipping container and a method of assembly of the building structure. The modular beam structure and modular base structure each include a frame, which interlock with each other and a shipping container by corner castings with twist lock assemblies, which are arranged in a particular orientation with each other. The modular base structure is supported by the corner castings of a shipping container and the base structure supports an end portion of at least one modular beam structure. At least one modular beam structure spans a distance between spaced shipping containers. The modular beam structures can be used as roof trusses and are sized to be transported on top of each other or overlap with each other, in side of shipping containers.