public ShapeDescription ShapeDescription {get;}

// 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> { { "Copper", "C_1" },
    { "Steel", "S_2" } })
{
  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)
{ DomainDescription = 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;
}