public static FieldDescription CreateDomainField( 
   string name,
   DomainDescription domainDescription
)

{
  // 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 AddFieldWithDomainSnippet(Geodatabase geodatabase)
  {
    //The FeatureClass to add field
    string featureClassName = "Pipes";

    SchemaBuilder schemaBuilder = new SchemaBuilder(geodatabase);

    // Create a CodedValueDomain description for water pipes
    CodedValueDomainDescription pipeDomainDescription = new CodedValueDomainDescription("WaterPipeTypes",
      FieldType.String, new SortedList<object, string>
      {
          { "C_1", "Copper" },
          { "S_2", "Steel" }
      })
    {
      SplitPolicy = SplitPolicy.Duplicate,
      MergePolicy = MergePolicy.DefaultValue
    };

    // Create a coded value domain token
    CodedValueDomainToken codedValueDomainToken = schemaBuilder.Create(pipeDomainDescription);

    // Create a new description from domain token
    CodedValueDomainDescription codedValueDomainDescription = new CodedValueDomainDescription(codedValueDomainToken);

    // Create a field named as 'PipeType' using a domain description
    FieldDescription domainFieldDescription = new FieldDescription("PipeType", FieldType.String);
    domainFieldDescription.SetDomainDescription(codedValueDomainDescription);

    //Retrieve existing information for 'Pipes' FeatureClass
    FeatureClassDefinition originalFeatureClassDefinition = geodatabase.GetDefinition<FeatureClassDefinition>(featureClassName);
    FeatureClassDescription originalFeatureClassDescription =
      new FeatureClassDescription(originalFeatureClassDefinition);

    // Add domain field on existing fields
    // Adding a field,'PipeType', which uses the coded value domain to the 'Pipes' FeatureClass
    List<FieldDescription> modifiedFieldDescriptions = new List<FieldDescription>(originalFeatureClassDescription.FieldDescriptions)
      { domainFieldDescription };

    // Create a new description with updated fields for 'Pipes' FeatureClass 
    FeatureClassDescription featureClassDescription = new FeatureClassDescription(originalFeatureClassDescription.Name, modifiedFieldDescriptions,
      originalFeatureClassDescription.ShapeDescription);

    // Update the 'Pipes' FeatureClass with domain field
    schemaBuilder.Modify(featureClassDescription);

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

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