Add the data model for structures and prevent them from being embedded in most actors.

module/documents/Item/Structure.mjs

@@ -0,0 +1,23 @@
+import { ItemHandler } from "./Handler.mjs";
+
+/** @this {ItemHandler} */
+async function _preCreate() {
+	if (this.isEmbedded) {
+		let actor = this.actor;
+		if (actor.type === "settlement") {
+			return await actor.preItemEmbed(this);
+		};
+		ui.notifications.error(
+			game.i18n.format(
+				`dotdungeon.notification.error.cant-embed-item`,
+				{ item: this, actor }
+			),
+			{ console: false, }
+		);
+		return false;
+	};
+};
+
+export default {
+	_preCreate,
+};