There is no single correct number of screws per metre for every panel. Panel data, supports and loads are required. Only from the fixing design can the quantity for ordering be derived. An average per m² helps logistically but does not determine the layout. On walls and roofs, it is also important to distinguish between main fasteners and secondary connections. You can ask about a square metre of surface area, a linear metre of panel or a linear metre of joint. These are different bases for calculation. For a panel 1 m wide, the first two figures may be equal, but with a different module they are not. Always state the unit and the fixing scope.