SELECT
  table_id AS TABLE_NAME,
  ROUND(size_bytes / (1024 * 1024), 2) AS size_mb
FROM
  `project_id.dataset_id.__TABLES__`
ORDER BY
  size_bytes DESC

で取得できる。project_idとdataset_idの部分については環境に応じて書き換える。

SELECT
  storage_tier,
  SUM(total_billable_bytes) billable_bytes
FROM
  `project_id.dataset_id.INFORMATION_SCHEMA.PARTITIONS`
GROUP BY
  storage_tier