public FeatureDatasetDescription( 
   string name,
   SpatialReference spatialReference
)

public void CreateFeatureDatasetSnippet(Geodatabase geodatabase)
{
  // Creating a FeatureDataset named as 'Parcel_Information'

  SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

  // Create a FeatureDataset named as 'Parcel Information'
  FeatureDatasetDescription featureDatasetDescription =
    new FeatureDatasetDescription("Parcel_Information", SpatialReferences.WGS84);
  schemaBuilder.Create(featureDatasetDescription);

  // Build status
  bool buildStatus = schemaBuilder.Build();

  // Build errors
  if (!buildStatus)
  {
    IReadOnlyList<string> errors = schemaBuilder.ErrorMessages;
  }
}