This study is focused on the efficient use of cross-ventilation in a densely populated area by using roof windows in particular. Wind tunnel experiments were conducted to understand not only the relation between the building coverage ratio and the coefficient of wind pressure (C p) but also the relation between the roof slope of a residence and C p value. To simulate an urban area, dummy models were placed around a target model, and the building densities were set to 0, 10, 20, and 40%. The roof slopes of residences were set to 0° (flat roof), 15°, and 26.7°. The C p distribution on the surface of each residential model was measured. The tangential dynamic pressure at the openings was also measured to predict the cross-ventilation rate (Q value) by using a local dynamic similarity model, and the calculated Q value was compared with the experimental value. The experiments and calculations revealed the following information: (1) the overall C p value of a flat roof residence approaches zero when the building coverage ratio increases; (2) a negative pressure is maintained near the ridge of a leeward roof, even if the building coverage ratio increases to 40%; and (3) the efficient use of the negative pressure near the ridge on the leeward roof can improve the cross-ventilation rate in a densely populated area.