A commercial fit-out scope split - Cat A delivers a basic finished shell (raised floors, ceilings, basic MEP) ready for occupation, and Cat B is the tenant-specific layer (partitions, furniture, branding) built on top of it. A landlord's model typically stops at Cat A, and the tenant's fit-out contractor picks up from there in their own Cat B model - meaning the two models need clean, well-defined interfaces (a shared coordinate system and a clear scope boundary) even though they're built at completely different times by completely different teams.