(This question is a follow-up to this comment thread.)
I came across the sentence 家が火事だよ,† and although the meaning is clear from context, I'm struggling to understand what's going on grammatically. Specifically, the use of が makes me inclined to translate it as e.g. "Your house is a conflagration!", which sounds awkward (and also very dire) compared to the correct translation of "The house is on fire!".
Is this the same construction as how one might say 私がウナギです to a waiter to mean "I ordered the eel."? To wit, should I interpret the sentence à la 家(の何々)が火事だよ (for an appropriate choice of 何々)?
If that's not correct, however, is there a general way I can understand sentences like this (assuming that there are indeed others like it)?
†I specifically saw it on Duolingo, so I took it with a grain of salt at first. But, Weblio also shows it in a few of its corpuses, so it seems to be natural after all.