Sometime reading the user manual could help...
Importing the data using DXF or TXT format is not enough: I mean in this way you just imported the data describing the terrain but you still don't get the terrain model.
You have to define the terrain perimeter by using the Ourline tool and then build the terrain using the Terrain tool.
Friendly
Fabrizio
Fabrizio Diodati
Graphisoft Italy Srl | Via Rossignago 2/A Spinea Venezia 30038 Italy