Tell them your building size and what the length of the overhang you want. Your
final trusses will be longer then 20' . They do need to know the exact building
size so the span cross braces are long enough which it sounds like will be 20'
My wood shop was 20x20 so it ended up being 9 trusses and 2 gable ends. The
overhead was 14'' on each side which is common here.