In simple terms its a fibre glass car so no two mesurements side to side are going to be the same.

Even classic corvettes vary quite alot side to side. In front arches are not in quite the same place but you do not notice unless you go looking for it. windscreen gap that really depends on how it has been trimmed, I have seen some worse than others, and its always interesting to see how different people have treated the a pillar area, some a straight,some have more shape to their trim.
There are not any real hard and fast rules, just make it look right
Neil