You can define a mask block by selecting a closed polyline in the drawing and defining it as a mask block, by copying and editing an existing mask block, or by using the AEC Content Wizard.
Use the AEC Content Wizard to save mask blocks in content drawings for convenient reuse.
To create, edit, copy, or purge mask block definitions, use the Style Manager. The Style Manager provides a central location in AutoCAD Architecture 2024 toolset, where you can work with definitions and styles from multiple drawings and templates.