It’s just a coincidence that the same words are homonyms in English and German in this case: “Warehouses” = “Warenhäuser”, “There were houses” = “Dort waren Häuser”. You don’t even have to translate to colloquial German as the other comment suggests, a word-by-word translation works here.

So I went and googled it out of curiosity, after remembering that German for was/were (in some form anyway) is ‘war’.

I found this in a thread about Downfall and a translated joke where someone was wondering what the original was:

The German pun uses ‘Warenhaus’ department store and “Da war 'n Haus” - “there was/used to be a house”.