A composite building system comprising a structural frame, walls, floor, and roof is made of pultrusion fiber reinforced polymer (PFRP) material. A combination of PFRP, stainless steel screws and flexible epoxy can be used in the manufacture of a mobile or fixed structure. During assembly, an intumescent fire barrier can be applied to the PFRP components. Unlike traditional building materials, an exterior waterproof finish coating is not required when using a PFRP wall, floor, and roof assembly. The PFRP wall and wall assembly can be used with both PFRP structural framing and traditional framing materials, such as concrete, steel, or wood, allowing the PFRP wall and wall assembly to be used as a mid-rise or high-rise curtain wall.