I don't think there is a specific "order" I just try and keep my parts close together. I don't think it is a good idea, for example, to have your front wing at 60% while the other parts of your car are at 35%.
I always tend to focus on how much each part costs to replace... the idea being that the more expensive the part, the more important it is :)
Chassis 200,000
Internals 150,000
Sidepods 25,000
Front wing 20,000
Rear wing 15,000
Suspension 15,000
Underbody 10,000
Well, if it is more expensive it doesn't mean that it is more important. In a real F1 car, the front and rear wings are by far more important than the sidepods. The internals are expensive because everything inside has to be redesigned and re-fitted, not because you will get more downforce, better ballance or performance out of it.
I recall a thread where the consensus was that you were as slow as your least developed part, therefore it would be better to keep them roughly the same level.
