Complete the design. Before importing a mass to Revit, complete as much of the design as required in the design software. If you make changes to the design after importing it to Revit, you cannot update the Revit family or project with the changes.
Level of detail. Before importing a mass to Revit, reduce the amount of detail that it contains. For example, cornices, roof eaves, window detail, reveals, windows, casework, tessellated approximations of surfaces, ornaments and articulation on walls, and other such fine work can be imported as separate families. After importing the simplified mass to Revit, you can then add these details to the walls and roofs created from the mass.
Mass floors. If a mass family imports only non-volumetric geometry, you cannot create mass floors in Revit. However, if an imported mass family contains both volumetric and non-volumetric geometry, you will be able to create mass floors from the volumetric portions of the geometry. (You will also receive warnings. You can ignore those.)