Waveguide slot array antennas can have high gain, since the power distribution network (waveguide) has low loss, enabling a large aperture size. Rapid response to requirements for frequency, gain, and skew angle inspired a search for an alternative to conventional, commercial slot array acquisition. The solution to this requirement is high-resolution 3-D printing of modified slot arrays combined with metal plating. Modification of the structure included removal of wall material in regions where these openings would not cause radiation, opening the structure to enable metal plating while not affecting gain. A 3-D-printed slot array requires no further assembly, unlike conventional waveguide-based arrays that require soldering or brazing, block machining, or plate assembled, brazed structures. Stereolithography 3-D printing of plastic slot array antennas, modified to enable metal plating, has been used to produce a 30 dBi realized gain slot array at 21 GHz for under $1000 USD in a few weeks. Metal plated, 3-D printed plastic slot arrays are also very lightweight in comparison with conventional metal structures. Performance of 3-D printed, metal plated slot arrays has been shown to be identical to conventional metal structures at frequencies up to 22 GHz.