public ShapeDescription ShapeDescription {get;}

public void AddFieldWithDomainSnippet(Geodatabase geodatabase)
{
    // Adding a field,'PipeType', which uses the coded value domain to the 'Pipes' FeatureClass

    //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
    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;
    }
}