We described and ran a lesson plan for a build-your-own visible-range spectrophotometer undergraduate project as inspired by the research of Bougot-Robin, Imperial College London. Students were required to improve a basic Raspberry Pi spectrophotometer design and evaluate their improvements. Students learned firsthand how to manage instrumental error by fixing component distances and minimizing stray light, while modifying their Python scripts to process and plot their collected data. Students evaluated the quality of their instrument prototypes by quantifying the limits of detection, quantification, and linearity, or by attempting to reproduce the visible spectrum of aqueous methylene blue solution. As part of the key findings of this work, we found that student ability to draw a diagram of a spectrophotometer has improved by an effect size of Hedges' g = +2.25 by the end of the semester, compared to g = -0.05 for students who took traditional chemistry lab classes instead.