Can you clarify what you mean by "overlapping"? What style of armor are you building?
If you are talking about trauma plating (a base plate with another, slightly smaller plate mounted on top of it) you are better off shaping the base plates first. Once these are shaped, you can heat the trauma plates to shape on the existing plate. Once they are shaped and sanded to your preference, you can then glue the trauma plate to the existing plate. This is far easier than trying to glue them first. If you glue them first, you will not be able to shape it the way you want and it will cause you problems.
