From Longman Dictionary of Contemporary Englishunder the same roof/under one roofunder the same roof/under one roofTOGETHERin the same building or home If we’re going to live under the same roof, we need to get along. Here you can buy food, clothes, and electrical goods all under one roof. → roof
Examples from the Corpus
live under the same roof• She only knew she was bitterly disappointed that she and Seb would not be living under the same roof.• Yet Shaker men and women lived under the same roof in large dormitory-like houses. 