Capture the interfaces
List contact surfaces, fasteners, seals, tolerances and service access. These details often control the usefulness of a component more than its exterior appearance.
Select a realistic prototype
Match the prototype method to the behaviour under investigation. A visual model may not represent the mechanical or thermal response of a production part.
Agree the next decision
Define the measurements that will support a design change, tooling commitment or additional test. Keep the result tied to that decision.