Military infrastructure development plays a key role in national defense strategy, including modern methods like precast modular systems. However, the implementation of this method involves high risks—especially when working at heights and handling heavy components—which can lead to accidents and poor project performance. This mixed-method research aims to analyze significant criteria that influence the selection of upper structure construction methods in military building projects. The qualitative phase employed a Systematic Literature Review (SLR) to formulate the main variables, which were then validated using the Delphi technique and a pilot survey. Subsequently, a quantitative survey involving 100 respondents was conducted, followed by multiple linear regression analysis to assess the significance of each criterion. The results identified nine significant variables (p < 0.001): cost (42.98%), sustainability (26.97%), risk (10.55%), time (5.73%), environmental conditions (4.70%), resource availability (2.75%), technical aspects (2.40%), Building Information Modeling (BIM) (2.32%), and quality (1.96%). The model’s coefficient of determination reached R2 = 0.887, indicating that 88.7% of the variation in method selection can be explained by these variables. These findings provide valuable insights for stakeholders in selecting effective and safe construction strategies and offer a foundation for further research on advanced construction methods.