Sindh is currently experiencing a significant transformation through various building projects aimed at enhancing infrastructure, energy supply, and resilience against natural disasters. However, cost overruns on these projects remain a critical concern. Cost overruns are a common issue within the construction industry, which severely affects economic growth and project success rates in Pakistan, particularly in Sindh Province. This study investigates the key factors contributing to cost overruns in building construction projects in Sindh. To collect data, questionnaire surveys were designed for employees involved in these projects, and the responses were analyzed using the Average Index method. Key factors identified as contributing to cost overruns include delays in payments, re-work, labor shortages, late procurement of materials, rising material costs, inexperienced contractors, financial difficulties faced by contractors, and financial claims. The study’s recommendations, such as enhancing communication processes and on-site client representation, are practical and actionable, offering stakeholders a roadmap to mitigate cost overruns and ensure successful project completion.