This research presents the impact on surface roughness of build orientation in the fabrication of a 3D metal printed X-band horn antenna (8.2-12.4 GHz). Build orientation is investigated by printing the antenna at three different orientations of 45, 90 and 180, with respect to the building platform. The results indicate that the build orientation has an impact on the surface roughness, though not affecting its transmission coefficient in the X-band. The horn antennae are fabricated with Maraging Steel (MS1), using the Direct Metal Laser Sintering (DMLS) technique on an EOS M280 system. The variations in the microstructural surface roughness due to the build orientation are measured using a White Light Interferometer (WLI). The investigation proved that there is no significant effect of the orientation on the gain of the antenna while working in the X-band. However, the changes could be significant if working at higher frequencies, where this magnitude of surface roughness is more significant.