In OpenBuildings Designer each WorkSet must contain a BB_Floormaster.dgnlib to store floors and grid systems.
This file is specified by the variable BB_FLOORMASTER_DGN and is located by default in the WorkSet Dgnlib folder.
A WorkSet can contain one or more buildings (depending on how you organize your projects). If a WorkSet contains multiple buildings the Floor Manager and Grid Systems Manager can be used to create multiple sets of floors and grids with the appropriate offsets and rotations.
In Floor Manager, a rotation can be applied to floors but offsets are not needed as the floors are simply reference planes with unlimited extents:
Both offsets and rotations must then be applied to Grid Systems (for completeness this example shows floors at different rotations, which will not apply to most buildings):
Grids can also be rotated by snapping to underlying or referenced geometry:
Floor Management - Changing the name of BB_FloorMaster.dgnlib