public static FieldDescription CreateObjectIDField()

{
  // Must be called within QueuedTask.Run
  void CreateTableSnippet(Geodatabase geodatabase, CodedValueDomain inspectionResultsDomain)
  {
    // Create a PoleInspection table with the following fields
    // GlobalID
    // ObjectID
    // InspectionDate (date)
    // InspectionResults (pre-existing InspectionResults coded value domain)
    // InspectionNotes (string)

    // This helper routine creates a FieldDescription for a GlobalID field with default values
    FieldDescription globalIDFieldDescription = FieldDescription.CreateGlobalIDField();

    // This helper routine creates a FieldDescription for an ObjectID field with default values
    FieldDescription objectIDFieldDescription = FieldDescription.CreateObjectIDField();

    // Create a FieldDescription for the InspectionDate field
    FieldDescription inspectionDateFieldDescription = new FieldDescription("InspectionDate", FieldType.Date)
    {
      AliasName = "Inspection Date"
    };

    // This helper routine creates a FieldDescription for a Domain field (from a pre-existing domain)
    FieldDescription inspectionResultsFieldDescription = FieldDescription.CreateDomainField("InspectionResults",
      new CodedValueDomainDescription(inspectionResultsDomain));
    inspectionResultsFieldDescription.AliasName = "Inspection Results";

    // This helper routine creates a FieldDescription for a string field
    FieldDescription inspectionNotesFieldDescription =
      FieldDescription.CreateStringField("InspectionNotes", 512);
    inspectionNotesFieldDescription.AliasName = "Inspection Notes";

    // Assemble a list of all of our field descriptions
    List<FieldDescription> fieldDescriptions = new List<FieldDescription>()
      {
        globalIDFieldDescription, objectIDFieldDescription, inspectionDateFieldDescription,
        inspectionResultsFieldDescription, inspectionNotesFieldDescription
      };

    // Create a TableDescription object to describe the table to create
    TableDescription tableDescription = new TableDescription("PoleInspection", fieldDescriptions);

    // Create a SchemaBuilder object
    SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

    // Add the creation of PoleInspection to our list of DDL tasks
    schemaBuilder.Create(tableDescription);

    // Execute the DDL
    bool success = schemaBuilder.Build();

    // Inspect error messages
    if (!success)
    {
      IReadOnlyList<string> errorMessages = schemaBuilder.ErrorMessages;
      //etc.
    }
  }
}

{
  // Must be called within QueuedTask.Run
  void CreateFeatureClassSnippet(Geodatabase geodatabase, FeatureClass existingFeatureClass,
    SpatialReference spatialReference)
  {
    // Create a Cities feature class with the following fields
    // GlobalID
    // ObjectID
    // Name (string)
    // Population (integer)

    // This helper routine creates a FieldDescription for a GlobalID field with default values
    FieldDescription globalIDFieldDescription = FieldDescription.CreateGlobalIDField();

    // This helper routine creates a FieldDescription for an ObjectID field with default values
    FieldDescription objectIDFieldDescription = FieldDescription.CreateObjectIDField();

    // This helper routine creates a FieldDescription for a string field
    FieldDescription nameFieldDescription = FieldDescription.CreateStringField("Name", 255);

    // This helper routine creates a FieldDescription for an integer field
    FieldDescription populationFieldDescription = FieldDescription.CreateIntegerField("Population");

    // Assemble a list of all of our field descriptions
    List<FieldDescription> fieldDescriptions = new List<FieldDescription>()
        { globalIDFieldDescription, objectIDFieldDescription, nameFieldDescription, populationFieldDescription };

    // Create a ShapeDescription object
    ShapeDescription shapeDescription = new ShapeDescription(GeometryType.Point, spatialReference);

    // Alternatively, ShapeDescriptions can be created from another feature class.  In this case, the new feature class will inherit the same shape properties of the existing class
    ShapeDescription alternativeShapeDescription = new ShapeDescription(existingFeatureClass.GetDefinition());

    // Enable support for measure (M) value, if needed
    // shapeDescription.HasM = true;

    // Enable support for the vertical coordinate system (Z), if needed
    // shapeDescription.HasZ = true;

    // Create a FeatureClassDescription object to describe the feature class to create
    FeatureClassDescription featureClassDescription =
      new FeatureClassDescription("Cities", fieldDescriptions, shapeDescription);

    // Create a SchemaBuilder object
    SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

    // Add the creation of the Cities feature class to our list of DDL tasks
    schemaBuilder.Create(featureClassDescription);

    // Execute the DDL
    bool success = schemaBuilder.Build();

    // Inspect error messages
    if (!success)
    {
      IReadOnlyList<string> errorMessages = schemaBuilder.ErrorMessages;
      //etc.
    }
  }
}