When I started in the Art Dept, I worked as an Art Dept Assistant for years. I was fortunate to have reeceived several model making assignments. Models are particularly useful when building an organic set, like a cave, that would otherwise be hard to draw.
One model in particular was, however, a hard lesson learned.
I had built this beautiful model and painted it. The Designer approved it and it went to the shop. Later he told me that it needed to be repainted to look like a different rock type. I went down to the shop to paint it as asked. I based out the model in black and left it to dry before adding my light greys. My own personal model method.
Then 'Film" happened. I can't remember exactly the string of events, but I diddn't get back to the model in time.
Suddenly I had one very upset Designer on my hands and a full size black set on the stage.
Models are great. But here's what I learned: make sure they are right when you leave them in the shop. Shop people take our designs very literally. And painters can cover a large area in no time with a spray machine.
Right: My Model before the damned revision