This course provides a foundational overview of commercial roofing systems and assemblies, building on concepts introduced in prior C.R.E.W. courses (101–301). The course connects roofing fundamentals such as deck types, insulation options, membrane systems, and attachment methods to the broader design and specification process used by Registered Design Professionals. Participants are introduced to how roofing systems are evaluated for performance, code compliance, and constructability, with an emphasis on understanding the why behind common design criteria. The course also establishes a bridge to advanced design-focused topics covered in C.R.E.W. 402 by introducing key considerations related to wind resistance, fire testing, laboratory verification, and the role of specifications, standards, and warranties in the overall roofing system design.