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;
    }
}