Topside modules are fabricated at a production site using as a foundation for installation a gravity-based structure (GBS), which can stay afloat during water transportation. Modules fabrication includes: Stage I, fabrication of components; Stage II, fabrication of nodes from the components; Stage III, fabrication of sub-assemblies from the nodes; Stage IV, shotblasting and painting of assemblies; and Stage V, assembling modules from the assemblies. Then modules transportation, movement to their seats on the GBS and their integration include: Stage VI, moving the modules to an area near the dock using self-propelled vehicles. Stage VII, moving each module onto guides of a lifting system installed in a dry dock. Stage VIII, lifting each module until lifting system guides are connected with GBS top slab guides. Stage IX, moving each module to its seat on the GBS, installed on the GBS and integrated with other modules and the GBS.