public FeatureClassToken Create( 
   FeatureDatasetDescription featureDatasetDescription,
   FeatureClassDescription featureClassDescription
)

// Creating a FeatureDataset named as 'Parcel_Information' and a FeatureClass with name 'Parcels' in one operation

string featureDatasetName = "Parcel_Information";
string featureClassName = "Parcels";

SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

// Create a FeatureDataset token
FeatureDatasetDescription featureDatasetDescription = new FeatureDatasetDescription(featureDatasetName, SpatialReferences.WGS84);
FeatureDatasetToken featureDatasetToken = schemaBuilder.Create(featureDatasetDescription);

// Create a FeatureClass description
FeatureClassDescription featureClassDescription = new FeatureClassDescription(featureClassName,
  new List<FieldDescription>()
  {
    new FieldDescription("Id", FieldType.Integer),
    new FieldDescription("Address", FieldType.String)
  },
  new ShapeDescription(GeometryType.Point, SpatialReferences.WGS84));

// Create a FeatureClass inside a FeatureDataset
FeatureClassToken featureClassToken = schemaBuilder.Create(new FeatureDatasetDescription(featureDatasetToken), featureClassDescription);

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

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

// Creating a FeatureClass named as 'Tax_Jurisdiction' in existing FeatureDataset with name 'Parcels_Information'
string featureDatasetName = "Parcels_Information";
string featureClassName = "Tax_Jurisdiction";

// Create a FeatureClass description
FeatureClassDescription featureClassDescription = new FeatureClassDescription(featureClassName,
  new List<FieldDescription>()
  {
    new FieldDescription("Tax_Id", FieldType.Integer),
    new FieldDescription("Address", FieldType.String)
  },
  new ShapeDescription(GeometryType.Point, SpatialReferences.WGS84));

FeatureDatasetDefinition featureDatasetDefinition = geodatabase.GetDefinition<FeatureDatasetDefinition>(featureDatasetName);

SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

// Create a FeatureClass inside a FeatureDataset using a FeatureDatasetDefinition
schemaBuilder.Create(new FeatureDatasetDescription(featureDatasetDefinition), featureClassDescription);

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

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