The effect of roof pitch angle on the buckling capacity of cylindrical shells when subjected to uniform external pressure was investigated numerically. Thirty-six cylindrical shells were modelled in ABAQUS CAE, with the modelled shells having various length-to-radius ratios of L/R = 0.5, 1, 2, and 4, various radius-to-thickness ratios R/T = 300, 500, and 1000, and various roof pitch angles of θ = 0, 15, and 30. The buckling mode and buckling capacity of the cylindrical shells were obtained. The results showed that the buckling capacity of the shells increased with decreasing the R/T and L/R ratios and increasing the roof pitch angle. Additionally, the results showed that when the cylindrical shells had R/T = 300 and L/R = 0.5, 1, and 2, a significant shell’s structural gain was obtained with minimum use of extra materials by increasing the roof pitch angle.