Dictionary / Vocabulary / 屋上屋を架す
おくじょうおくをかす
to do something useless; to gild the lily; to gild refined gold; to build a roof atop the roof
同じことを何回繰り返すの。屋上屋を架すようなくどい説明は勘弁してよ。
You're wasting your time with all this needless repetition, so spare us the long-winded explanation.