Ideally you would build your art files to be the full 100% print size. This assures the size of the final printed product is correct and the quality is as intended. Designers scale art primarily because large format graphic files become larger than their computer can handle. The solution is to build the art smaller with twice the resolution so the printer can enlarge the file to the proper size and resolution. When you need to do this, make sure your math is correct for both resolution and scale so that the result is a print ready art file, at the correct size, and with a minimum PPI of 150.