public AttributeIndexDescription( 
   Index attributeIndex,
   TableDescription tableDescription
)

{
  // Must be called within QueuedTask.Run
  void CreatingTableWithIndex(SchemaBuilder schemaBuilder)
  {
    FieldDescription nameFieldDescription = FieldDescription.CreateStringField("Name", 50);
    FieldDescription addressFieldDescription = FieldDescription.CreateStringField("Address", 200);

    // Creating a feature class, 'Buildings' with two fields
    TableDescription tableDescription = new TableDescription("Buildings",
      new List<FieldDescription>() { nameFieldDescription, addressFieldDescription });

    // Enqueue DDL operation to create a table
    TableToken tableToken = schemaBuilder.Create(tableDescription);

    // Creating an attribute index named as 'Idx'
    AttributeIndexDescription attributeIndexDescription = new AttributeIndexDescription("Idx", new TableDescription(tableToken),
      new List<string> { nameFieldDescription.Name, addressFieldDescription.Name });

    // Enqueue DDL operation to create an attribute index
    schemaBuilder.Create(attributeIndexDescription);

    // Execute build indexes operation
    bool isBuildSuccess = schemaBuilder.Build();
  }
}

{
  // Must be called within QueuedTask.Run
  void RemoveAttributeIndex(SchemaBuilder schemaBuilder, FeatureClassDefinition featureClassDefinition, string attributeIndexName)
  {
    // Find a index to be removed 
    ArcGIS.Core.Data.Index indexToRemove = featureClassDefinition.GetIndexes().First(f => f.GetName().Equals(attributeIndexName));

    // Index description of the index to be removed 
    AttributeIndexDescription indexDescriptionToRemove = new AttributeIndexDescription(indexToRemove, new TableDescription(featureClassDefinition));

    // Enqueue the DDL operation to remove index 
    schemaBuilder.Delete(indexDescriptionToRemove);

    // Execute the delete index operation
    bool isDeleteIndexSuccess = schemaBuilder.Build();
  }
}

{
  // Must be called within QueuedTask.Run
  void AddingIndexes(SchemaBuilder schemaBuilder, FeatureClassDefinition featureClassDefinition)
  {
    // Field names to add in the attribute index
    string fieldName = featureClassDefinition.GetFields().First(f => f.AliasName.Contains("Name")).Name;
    string fieldAddress = featureClassDefinition.GetFields().First(f => f.AliasName.Contains("Address")).Name;

    // Creating an attribute index with index name 'Idx' and two participating fields' name
    AttributeIndexDescription attributeIndexDescription = new AttributeIndexDescription("Idx",
      new TableDescription(featureClassDefinition), new List<string> { fieldName, fieldAddress });

    // Enqueue DDL operation for an attribute index creation 
    schemaBuilder.Create(attributeIndexDescription);

    // Creating the spatial index 
    SpatialIndexDescription spatialIndexDescription = new SpatialIndexDescription(new FeatureClassDescription(featureClassDefinition));

    // Enqueue DDL operation for the spatial index creation
    schemaBuilder.Create(spatialIndexDescription);

    // Execute build indexes operation
    bool isBuildSuccess = schemaBuilder.Build();

    if (!isBuildSuccess)
    {
      IReadOnlyList<string> errors = schemaBuilder.ErrorMessages;
      // Iterate and handle errors 
    }
  }
}