Achieving cost and time efficiency without compromising structural quality remains a key goal in construction projects. In practice, reinforced concrete (RC) structures are often overdesigned, resulting in material inefficiency and increased project duration. This study investigates a pre-construction design modification of a real public library project in Padang, Indonesia, in which the superstructure originally planned in RC was converted to a steel structure to meet accelerated completion targets set by the client. The modification was conducted using a Building Information Modeling (BIM)-integrated workflow to ensure accurate modeling, analysis, and coordination. Structural analysis was carried out using Robot Structural Analysis Professional (RSAP), followed by detailed 3D modeling and quantity takeoff in Autodesk Revit. Construction sequencing and scheduling simulations were performed using Navisworks Manage and Microsoft Project. The analysis revealed that the steel structure, while 20% more expensive in material cost (IDR 28,021,934,000 versus IDR 23,351,650,000 for RC), reduced the construction duration by 68 days (179 versus 247 days). Furthermore, the reduced structural weight of the steel system indicated potential savings in foundation dimensions and construction time, contributing to broader project efficiency. This study demonstrates the feasibility and benefits of structural system conversion in the pre-construction phase using BIM tools and emphasizes its relevance as a responsive strategy for managing dynamic project constraints.