How to create a geodatabase network dataset

// Create a new empty data element for a buildable network dataset.
IDENetworkDataset deNetworkDataset = new DENetworkDatasetClass();
deNetworkDataset.Buildable = true;

// Open the feature dataset and cast to the IGeoDataset interface.
IWorkspaceFactory workspaceFactory = new FileGDBWorkspaceFactory();
IWorkspace workspace = workspaceFactory.OpenFromFile(@
    "C:\Program Files\ArcGIS\DeveloperKit\SamplesNET\data\CreateNetworkDataset\Paris.gdb", 0);
IFeatureWorkspace featureWorkspace = (IFeatureWorkspace)workspace;
IFeatureDataset featureDataset = featureWorkspace.OpenFeatureDataset("RoadNetwork");
IGeoDataset geoDataset = (IGeoDataset)featureDataset;

// Copy the feature dataset's extent and spatial reference to the network dataset data element.
IDEGeoDataset deGeoDataset = (IDEGeoDataset)deNetworkDataset;
deGeoDataset.Extent = geoDataset.Extent;
deGeoDataset.SpatialReference = geoDataset.SpatialReference;

// Specify the name of the network dataset.
IDataElement dataElement = (IDataElement)deNetworkDataset;
dataElement.Name = "ParisNet";

// Create a new EdgeFeatureSource object and point it to the Streets feature class.
INetworkSource edgeNetworkSource = new EdgeFeatureSourceClass();
edgeNetworkSource.Name = "Streets";
edgeNetworkSource.ElementType = esriNetworkElementType.esriNETEdge;

// Set the edge feature source's connectivity settings.
IEdgeFeatureSource edgeFeatureSource = (IEdgeFeatureSource)edgeNetworkSource;
edgeFeatureSource.UsesSubtypes = true;
edgeFeatureSource.set_SubtypeConnectivityGroup(1, 1);
edgeFeatureSource.set_SubtypeConnectivityPolicy(1,
    esriNetworkEdgeConnectivityPolicy.esriNECPEndVertex);
edgeFeatureSource.set_SubtypeConnectivityGroup(2, 1);
edgeFeatureSource.set_SubtypeConnectivityPolicy(2,
    esriNetworkEdgeConnectivityPolicy.esriNECPEndVertex);
edgeFeatureSource.set_SubtypeConnectivityGroup(3, 1);
edgeFeatureSource.set_SubtypeConnectivityPolicy(3,
    esriNetworkEdgeConnectivityPolicy.esriNECPAnyVertex);

// Create a StreetNameFields object and populate its settings.
IStreetNameFields streetNameFields = new StreetNameFieldsClass();
streetNameFields.Priority = 1; // Indicates the primary street name.
streetNameFields.StreetNameFieldName = "FULL_NAME";

// Add the StreetNameFields object to a new NetworkSourceDirections object,
// then add it to the EdgeFeatureSource created earlier.
INetworkSourceDirections nsDirections = new NetworkSourceDirectionsClass();
IArray nsdArray = new ArrayClass();
nsdArray.Add(streetNameFields);
nsDirections.StreetNameFields = nsdArray;
edgeNetworkSource.NetworkSourceDirections = nsDirections;

// Create a new EvaluatedNetworkAttribute object and populate its settings.
IEvaluatedNetworkAttribute minutesAttribute = new EvaluatedNetworkAttributeClass();
INetworkAttribute2 minutesNetworkAttribute2 = (INetworkAttribute2)minutesAttribute;
minutesNetworkAttribute2.Name = "Minutes";
minutesNetworkAttribute2.UsageType = esriNetworkAttributeUsageType.esriNAUTCost;
minutesNetworkAttribute2.DataType = esriNetworkAttributeDataType.esriNADTDouble;
minutesNetworkAttribute2.Units = esriNetworkAttributeUnits.esriNAUMinutes;
minutesNetworkAttribute2.UseByDefault = true;

// Create evaluator objects and set them on the EvaluatedNetworkAttribute object.
INetworkFieldEvaluator ftMinutesNetworkFieldEvaluator = new
    NetworkFieldEvaluatorClass();
INetworkEvaluator ftMinutesNetworkEvaluator = (INetworkEvaluator)
    ftMinutesNetworkFieldEvaluator;
ftMinutesNetworkFieldEvaluator.SetExpression("[FT_Minutes]", "");
minutesAttribute.set_Evaluator(edgeNetworkSource,
    esriNetworkEdgeDirection.esriNEDAlongDigitized, ftMinutesNetworkEvaluator);

INetworkFieldEvaluator tfMinutesNetworkFieldEvaluator = new
    NetworkFieldEvaluatorClass();
INetworkEvaluator tfMinutesNetworkEvaluator = (INetworkEvaluator)
    tfMinutesNetworkFieldEvaluator;
tfMinutesNetworkFieldEvaluator.SetExpression("[TF_Minutes]", "");
minutesAttribute.set_Evaluator(edgeNetworkSource,
    esriNetworkEdgeDirection.esriNEDAgainstDigitized, tfMinutesNetworkEvaluator);

INetworkConstantEvaluator minutesNetworkConstantEvaluator = new
    NetworkConstantEvaluatorClass();
INetworkEvaluator minutesConstantNetworkEvaluator = (INetworkEvaluator)
    minutesNetworkConstantEvaluator;
minutesNetworkConstantEvaluator.ConstantValue = 0;
minutesAttribute.set_DefaultEvaluator(esriNetworkElementType.esriNETEdge,
    minutesConstantNetworkEvaluator);
minutesAttribute.set_DefaultEvaluator(esriNetworkElementType.esriNETJunction,
    minutesConstantNetworkEvaluator);
minutesAttribute.set_DefaultEvaluator(esriNetworkElementType.esriNETTurn,
    minutesConstantNetworkEvaluator);

// Add the attribute to the array.
attributeArray.Add(minutesAttribute);