<p>Roller coating is a widely used technique for architectural exterior wall painting; however, its mechanization and efficient implementation remain challenging. This study aimed to develop a water-based topcoat suitable for single-pass roller applications, achieving sufficient hiding power and high-quality finish without the intermediate drying required in conventional two-coat systems. Rheological analysis guided the control of paint viscosity at shear rates representative of roller applications, thereby improving roller stability, paint transfer efficiency, and slippage reduction. Rather than relying on a trial-and-error approach, we systematically identified rheological parameter ranges that simultaneously satisfy slip-free rolling, sufficient paint transfer, suppression of sagging from surface protrusions, and acceptable coating feel. This rational design approach increased the dry film thickness on protrusions, providing coverage comparable to that of conventional two-coat methods. Objective evaluations by skilled painters using image analysis, cross-sectional microscopy, and sensory scoring confirmed that the newly designed paint formulations maintained both ease of application and quality of appearance. This approach offers a rational framework for improving workability and process efficiency in architectural roller coatings, supporting labor reduction and the adoption of environmentally friendly materials.</p>