<p>The increasing emphasis on weight reduction for reduced fuel consumption and carbon emissions in the automotive sector has driven the demand for lightweight structural components that do not compromise stiffness. Current automotive aluminium hard-shell rooftop designs are typically polylithic, consisting of many interconnected parts joined by welding, riveting, bolting and adhesive bonding. This configuration results in increased weight, high manufacturing complexity, long production times, and potential leakage at joints. This created the need for the design of a lightweight monolithic (one piece) hard-shell rooftop that can be produced via the deep drawing process. This research presents a framework that integrates design, optimization, and manufacturing feasibility within a unified approach. The framework unifies theoretical, conceptual, and methodological elements to guide the systematic development of a lightweight monolithic structure. Its application culminated in the design and manufacture of a lightweight, monolithic hard-shell rooftop. This resulted in 30% weight reduction, 96% reduction in the number of sheet metal parts, 63% fewer manufacturing operations, and 95% shorter production time, while maintaining high stiffness-to-weight ratio, and eliminating leakage and the need for fasteners. The inclusion of optimized stiffness geometries ensured that mechanical performance was maintained despite significant weight reduction. This framework serves as a repeatable and transferable research reference model that can be applied to future lightweight monolithic hard-shell rooftops that seek to combine monolithic design, stiffness geometry optimization, manufacturing feasibility and the deep drawing of the physical prototype within a single decision-making framework.</p>