BuildSuite Core is a full-fledged construction ERP built on Frappe, already powering live projects for real builders, and now being open-sourced under Frappe incubation. This talk covers how it was built - starting with product thinking rather than a list of features. Every decision begins with the actual end user: understanding their perspective, turning the idea into a clickable, tangible prototype, getting client feedback on it, and only then building it out. This prototype-test-build loop is what allows a small team to ship robust software without constant rework.