Pattern making
A flat design is broken into pieces that can be cut and sewn. This establishes the physical silhouette and proportion.
Prototype and pattern revision
The prototype turns the pattern into the first physical object. Revision responds to what the object reveals about shape, proportion, expression and workmanship.
Approval sample and production reference
An approval sample records the agreed shape, color, materials and details. How it controls production should still be defined in project documents and approvals.
Why unit price is not the only question
Also ask what stage the project is in, what will serve as the production reference and how completed production will be checked.