Cost performance is the most important parameter that directs the projects viability. The construction cost-variation from the project budget is the key measure that expresses project performance. In spite of many literature, tools, arithmetic models, and data sources are available for computing the cost estimate, the cost-overrun keeps happening in projects. The previous researches in the construction cost-overrun domain reflect a typical pattern of investigation, that identify the significant factors for the cost-overrun, analyse from heterogeneous dataand develop a regression model for the forecast by assuming the causes are independent. The consideration of interrelationships among cost-overrun factors is very minimal. However, the cost-overrun in construction projects is usually an outcome of combining several interrelated causes, rather than a single cause. Hence, it is important to know how dynamically the construction cost-overrun factors that impact the project cost performance, are interrelated with each other. As a systematic approach, the cost-overrun is investigated through an extensive literature study andparticipatory observation method for the detailed understandings of on-site scenarios. The intention is to investigate the dynamics of cost-overrun factors and develop a model for identifying the most significant causes and early prediction of cost-risks in building projects during project execution. The interdependency is analysed with the degree of influence, the significance level of cost-overrun factors and the impact of change in one factor leading to others with the evolution of time, by developing a dynamic model through Fuzzy Cognitive Map (FCM)with their causal interactions. Three residential development projects are delineated for developing a real-time cost-overrun causal map to depict the complexities during site execution and management. It is found that the most direct causes are difficult to manage compared to other causes of cost-overrun and the degree of dependency of the cost-overrun factors are high along with the project progress. The results explain the comprehensive pattern of cost-risks that may appear during project execution, as the model generates results on (1) probable occurrence (2) sources of risk (3) impressibilities (4) consequences the effects of cost-overrun factors on a projectsperformance. Further, it can be applied in different decision-making problems such as corrective actions, preventing actions, forecasting behaviours, policy analysis, decision-makers opinions, preparedness assessment, and stakeholders collaboration. Hence, the proposed dynamic model will help practitioners to manage cost-risks and decision-making problems effectively and proactively