Despite the importance of housing as one of basic human need, making it available, affordable and accessible has been a major problem in the country and it has become a serious issue. Several efforts have been made to address the issue but the problem persists. This study therefore examines the influence of design on cost of housing construction and housing affordability. The study used both primary and secondary data; primary data was collected through administration of two (2) types of questionnaires on Ilobu Road, Government Reservation Area, Osogbo, Osun State Nigeria. The first was administered to 250 homeowners while the second was administered on 32 housing professionals. The study find out that housing design and cost of building materials has great influence on cost of housing construction. It also established that people do not often patronize professionals due to perceived high professional charges and do not comply with specification. The study concluded that there should be curriculum re-engineering in schools and training institutions in order to produce new generation of cost friendly designers in building industry. The findings of this study will assist both the housing investors as well as policy makers in decision making.