How to use the overall force coeff. and net pressure coef. for a canopy acc. to EN1991-1-4?

[Jay_Chen]

In EN1991-1-4 7.3, it's said:
(5)The overall force coefficient represents the resulting force. The net pressure coefficient represents
the maximum local pressure for all wind directions. It should be used in the design of roofing elements
and fixings.

Does it mean that：
The overall is used to design the columns and the supports connections, the stability of the whole structure against overturning and uplift;
The net pressure cefficient is used for the design of roofing elements and fixings for roofing elements.

Are purlins and rafters roofing elements?

 

[Klitor]

Purlins and rafters are designed to 'overall'.
But note that resultant overall force acts on 1/4 of rafter span (trapezoidal distribution) so edge purlins will be designed to higher wind force than interior purlins