Hi wish-bear,
This is all part of the learning process. There's no 'scale' to work to.
Can only talk about scenery design, but the tendency is to make things too big.
Best thing is to start by making something simple eg in EOD and make sure you DON'T use a fixed scale of 1. Use a variable scale (might be 1 for big objects which you will only want to adjust in units of 1, might be 0.25 if you want to work in units of .25 metre. Otherwise you can't adjust the size eg in FSSC or airport to see how things look by varying the final scale of the macro (see below).
So make your thing, pop it into a scenery and then land the Bell beside it. Imagine the pilot getting out and see how your thing would compare to his height.
I find that most 3rd party APIs I use which claim to be on a scale of 1 I have to reduce to something like 0.8 using the above method - and I prefer to believe my eyes!
See how you go. It's a fascinating business is scenery design
