C# .NET Sample Code: Create/Add a Custom Entity Field via Web Services

EntityCustomField customfield = new EntityCustomField();

customfield.internalId = "_ws_createdfield1";
customfield.label = "WS Created Custom Field 1";

customfield.fieldType = CustomizationFieldType._freeFormText;
customfield.fieldTypeSpecified = true;

customfield.storeValue = true;
customfield.storeValueSpecified = true;

customfield.appliesToCustomer = true;
customfield.appliesToCustomerSpecified = true;

customfield.appliesToVendor = true;
customfield.appliesToVendorSpecified = true;

WriteResponse writeResponse = _service.add(customfield);