Building projects as sub-sect of construction projects are complex and different in design and performance attributes. The prominent classes of building projects are high-rise residential buildings, hospitals, hotels, general offices, retail buildings/malls, educational institutions, and warehouses. In this study, building projects have been classified based on their end use. Complexities vary between construction projects and within various types of building projects, as well as across regions and countries. Understanding the sources of complexity is imperative to strategize their successful development. This research paper attempts to identify the sources of complexities using the design and performance attributes of seven prominent building types. A survey was conducted through experienced architects and construction professionals (the mean years of experience being approximately 13.88 years) over 34 different attributes or parameters under six categories. These attributes have been shortlisted from past research work by various authors, and the pilot study for this project. The Kruskal-Wallis Test was used to calculate the mean ranking and to confirm that the medians of each building type were not the same when compared against each attribute, irrespective of the level of complexity. Using data analysis and the mean ranking scores as a representation of relative complexity, primary sources of complexity in each class of buildings have been identified and listed. The results indicate that hospitals (as a building typology) are relatively the most complex building facilities in terms of design and performance attributes, showing the highest mean ranking towards 16 attributes (with only one shared ranking). Hospitals are followed by retail/malls (10 with one shared ranking), hotels (3), high-rise residential buildings (4), educational institutions (2), general offices (0), and warehouses (0). Strategies to manage these attributes have been proposed for each building typology so that the risks emanating from the complexities of these building projects can be mitigated and effectively managed at the design stage.