Other forms: mocked up; mocking up
To mock up is to make a model of something that will eventually be constructed. You might mock up the suit you've designed using inexpensive fabric before sewing the final version out of red velvet.
Engineers mock up prototypes of things like airplanes, spacecraft, and cars, building first-draft versions that will be tested and eventually improved upon in the final version. Furniture builders, game designers, and architects mock up drafts of their products as well. Sometimes these models are smaller than the real thing, or simply made from inexpensive materials. Newspapers, magazines, and books are mocked up, too, with photos and print laid out so they can be rearranged before they're printed.