To create a basic 3D block for Design Master Electrical, use the Create 3D Blocks command.
Ribbon: DME: Customization->Block Creation->Create 3D Block from Entities
Pulldown menu: DM Electrical->Customization->Block Creation->Create 3D Block from Entities
This command will take a polyline or circle and extrude it to make a very basic 3D block for you. It also helps you name the block correctly and creates it in the correct folder.
For more complicated 3D blocks, you will need to manually create them using standard AutoCAD commands. We recommend that the final block should contain 3D face entities, and not solids or anything else. We have found that 3D faces import best into other programs such as Navisworks and Revit.