Southwestern Nigeria lies within what has been classified as warm humid climate. This implies that design in terms of orientation of windows, quantity of sun radiation excluded from the indoor, choice of building materials for walls, windows, and roofs can be the same with or without little variation anywhere within the Southwestern Nigeria. There are variations of climate in various localities of the zone. Some of this variation may necessitate different design solutions. In this study, the climate data for six towns were obtained from Nigeria Metrological Agency. The data were quantitatively analysed using graphical and application of Mahoney method. Building design decisions for each of the towns was suggested based on the analysis.