Decision-making within a large corporation is a major catalyst for crises and disagreements among decision-makers. When contracting involves significant financial amounts, the choice between meeting the contractor’s expectations and the willingness to pay for these services can be a determining factor. Thus, this study reviews the importance of Multicriteria Decision Analysis (MCDA) methods in supporting decision-makers in complex processes. The study presents a case of prioritization of the contracting modality for building maintenance services in a Basic Sanitation Company. The methodology combines qualitative and quantitative approaches, including literature research, brainstorming, and Delphi analysis. The developed multicriteria model applies the MACBETH approach to assess the criticality of systems and specific points in a maintenance work order. As the first phase of the research, this study aims to identify criteria and sub-criteria considered essential for analysis. With expert participation and the application of Brainstorming and Web-Delphi methodologies, it was possible to construct the value tree necessary to structure the next phase of the decision support model based on multicriteria analysis.