We introduce MobiPrint, a prototype mobile fabrication system that combines elements from robotics, architecture, and Human-Computer Interaction (HCI) to enable environment-scale design and fabrication in ad-hoc indoor environments. MobiPrint provides a multi-stage fabrication pipeline: first, the robotic 3D printer automatically scans and maps an indoor space; second, a custom design tool converts the map into an interactive CAD canvas for editing and placing models in the physical world; finally, the MobiPrint robot prints the object directly on the ground at the defined location. Through a “proof-by-demonstration” validation, we highlight our system’s potential across different applications, including accessibility, home furnishing, floor signage, and art. We also conduct a technical evaluation to assess MobiPrint’s localization accuracy, ground surface adhesion, payload capacity, and mapping speed. We close with a discussion of open challenges and opportunities for the future of contextualized mobile fabrication.