Design frequently involves making tradeoffs to obtain the “optimal” solution to a design problem, often using intuition or past experience as a guide. Since vegetated roofing is a relatively complex and comparatively new technology to many practitioners, a rational, explicit method to help organize and rank the tradeoffs made during the design process is needed. This research comprises the creation of a framework diagramming the decision process involved in the selection of vegetated roofing systems. Through literature review, case studies and interviews with experts, the available knowledge is captured and organized to determine the critical parameters affecting design decisions. Six important evaluative categories are identified and parameters within these categories are addressed in the context of a decision support system for green roof designers. A summation of the total importance of the advantages represented by each alternative is used to determine the most feasible green roof system for a particular project. The framework is demonstrated and compared with green roof designers’ decision-making processes and conclusions are drawn regarding its effectiveness.