def METHOD_NAME(self):
    """
    G4 overloaded.
    Override the Construct method from G4VUserDetectorConstruction
    """
    # build the materials
    self.simulation_engine.simulation.volume_manager.material_database.initialize()
    # initial check (not really needed)
    self.simulation_engine.simulation.check_geometry()
    # build the tree of volumes
    volumes_user_info = self.world_volumes_user_info[gate.__world_name__]
    self.volumes_tree = gate.build_tree(volumes_user_info)
    # build all G4 volume objects
    self.build_g4_volumes(volumes_user_info, None)
    # return the (main) world physical volume
    self.is_constructed = True
    return self.g4_volumes[gate.__world_name__].g4_physical_volume