matrix-spec/data/event-schemas/examples/m.room.create.yaml

{
  "$ref": "core/state_event.json",
  "type": "m.room.create",
  "state_key": "",
  "content": {
    "creator": "@example:example.org",
    "room_version": "1",
    "m.federate": true,
    "predecessor": {
      "event_id": "$something:example.org",
      "room_id": "!oldroom:example.org"
    }
  }
}