A floor structure (1) of the type having "crossed reinforcement rods" is described comprising: a) a plurality of composite construction elements (2) arranged side by side and comprising: a1) an elongated body (3) made of expanded plastic material provided with an upper face (3a); a2) at least one reinforcing section bar (4) longitudinally extending in the elongated body (3) and having an upper portion (4c) protruding from the upper face (3a) of the body (3); b) a substantially reticular reinforcement metal structure (10) of a concrete casting (9), supported by the upper portion (4c) of the aforementioned at least one reinforcing section bar (4) at a predetermined distance from the upper face (3a) of the elongated body (3) made of expanded plastic material. Advantageously, the floor structure (1) exhibits lightness and self-supporting characteristics and allows to achieve a substantial reduction of the labor and costs for its manufacture.