Small, low-cost radar sensors offer a lighting independent sensing capability for indoor mobile robots that is useful for localization and mapping. Synthetic aperture radar (SAR) offers an attractive way to increase the angular resolution of small radar sensors for use on mobile robots to generate high-resolution maps of the indoor environment. This work quantifies the maximum synthesizable aperture length of our mobile robot measurement setup using radar-inertial odometry localization and offers insights into challenges for robotic millimeter-wave SAR imaging.