Saudi Arabia's giga-projects are expanding the scale, density, and technical complexity of building services systems. High-rise districts, hospitality destinations, airports, hospitals, cultural venues, and mixed-use communities require heating, ventilation and air-conditioning (HVAC), electrical, water, fire-safety, vertical transportation, security, and energy systems that remain reliable in harsh climatic and operational conditions. This review paper evaluates how digital monitoring and predictive maintenance can improve the operational performance of building services systems in Saudi mega projects. Following a review-paper structure inspired by recent Springer-style construction technology studies, the article synthesizes 2020-2025 literature on Building Information Modelling (BIM), Internet of Things (IoT), building management systems (BMS), digital twins, automated fault detection and diagnostics (AFDD), machine learning, and facility management. The study proposes a Saudi-oriented Digital Monitoring and Predictive Maintenance Framework (DMPMF) that links asset information requirements, sensor telemetry, analytics, work-order systems, and governance indicators. The review finds that the strongest value is achieved when predictive maintenance is treated not as a stand-alone algorithm, but as an information ecosystem connecting design handover, commissioning, operations, cybersecurity, workforce competence, and sustainability reporting. The paper contributes practical implementation stages, two conceptual visuals, and two synthesis tables for researchers, asset owners, consultants, and facility managers seeking Scopus/Q1-level alignment with Vision 2030 priorities.