I'm at a friend's house and I need to go to the bathroom. A couple of moments before I do, my friend hands me a roll of toilet paper, and I say: "I was just about to ask you if you had/have run out of toilet paper". I'd personally use "had" because of the tense agreement rule.
org/dictionary/english/toilet-roll
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Necrophagista roll of toilet paper,
This is also known as toilet roll https://dictionary.cambridge.org/dictionary/english/toilet-roll
NecrophagistI was just about to ask you if you had run out ...
As shown above.
CJ