Create a MassLevelData (Mass Floor) to associate a Level with a mass instance. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2012 
Syntax
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Parameters
- document
-  Type:  Autodesk.Revit.DB Document  
 The Document.
- massInstanceId
-  Type:  Autodesk.Revit.DB ElementId  
 The ElementId of the mass instance.
- levelId
-  Type:  Autodesk.Revit.DB ElementId  
 The ElementId of the Level to associate with the mass instance.
Return Value
The ElementId of the MassLevelData that was created, or the existing ElementId if it was already in added.Exceptions
| Exception | Condition | 
|---|---|
| Autodesk.Revit.Exceptions ArgumentException | The ElementId massInstanceId is not a mass instance. -or- The ElementId levelId is not a Level. | 
| Autodesk.Revit.Exceptions ArgumentNullException | A non-optional argument was NULL |