Scale of lighting fixture size to that of building?

Question:My mom is looking for lighting to put up around and in her barn that was just restored.

Does anyone have any information on a scale that would show for what size of building you'd need what size of lighting fixtures?

Answers:
No such scale exists. You have to define the objective of the lighting; is it architectural (i.e. for design effects only), functional (provide lighting for functional purpose), for security (light up the dark areas so bad guys don't have a place to hide)? Once you define the purpose of the lighting that will guide you in the choice of lighting.

Most any lighting store worthy of the name can help you, but that is the first question they will ask.