object/forum/1 matches the site

public static HumanMadeObject Uncertain_Attribution()
{
    var forum = new HumanMadeObject()
        .WithContext()
        .WithId("https://linked.art/example/object/forum/1")
        .WithLabel("Forum Romanum")
        .WithClassifiedAs(Aat.Painting, Aat.TypeOfWork);

    forum.IdentifiedBy = [new Name("Forum Romanum").AsPrimaryName()];

    forum.ProducedBy = new Production()
    {
        AttributedBy = [
            new AttributeAssignment()
            {
                ClassifiedAs = [ Aat.PossiblyBy ],
                Assigned = [
                    new Production()
                    {
                        CarriedOutBy = [
                            new Person()
                                .WithId("https://linked.art/example/person/corrodi")
                                .WithLabel("Salomon Corrodi")

                        ]
                    }
                ],
                AssignedProperty = "part"
            }
        ]
    };

    return forum;
}

• Metatype classification The second argument classifies the first, not the object: WithClassifiedAs(Aat.Description, Aat.Statement) says this is a Description, and Description is a kind of Statement. The Plain C# form shows the nesting.
• Role shortcuts AsPrimaryName, AsAccessionNumber and AsSystemAssignedNumber each add a single classification, with the AAT terms Primary Name, Accession Number and System Number.

var humanMadeObject = new HumanMadeObject
{
    Context = ["https://linked.art/ns/v1/linked-art.json"],
    Id = "https://linked.art/example/object/forum/1",
    Label = "Forum Romanum",
    ProducedBy = new Production
    {
        AttributedBy =
        [
            new AttributeAssignment
            {
                ClassifiedAs = [Aat.PossiblyBy],
                AssignedProperty = "part",
                Assigned =
                [
                    new Production
                    {
                        CarriedOutBy =
                        [
                            new Person
                            {
                                Id = "https://linked.art/example/person/corrodi",
                                Label = "Salomon Corrodi",
                            },
                        ],
                    },
                ],
            },
        ],
    },
    ClassifiedAs =
    [
        new Type("http://vocab.getty.edu/aat/300033618", "Painting")
        {
            ClassifiedAs = [Aat.TypeOfWork],
        },
    ],
    IdentifiedBy =
    [
        new Name("Forum Romanum")
        {
            ClassifiedAs = [Aat.PrimaryName],
        },
    ],
};

Generated from the object the example builds: every property that is set, as object initialisers, with the vocabulary constants where a term is in the registry. The fluent helpers are a convenience, not a requirement; this form and the one as written produce the same JSON.