A single sentence carries a lot of quiet longing here. The speaker imagines lying on a rooftop at night, and the only reason they'd be there is to write stories about someone else, telling them to the moon. The "if ever" makes it feel tentative, almost like a promise made to oneself, or a confession that the speaker isn't sure they'll act on.
What the speaker feels seems to be love or missing someone, though the poem never says so outright. The moon works as a silent listener, a safe place to put feelings that can't be said to the person directly. Writing "stories" instead of facts suggests the speaker would be inventing, remembering, or dreaming about this person, turning them into something larger than ordinary life.
The mood is soft, lonely, and romantic. It's nighttime, high up and alone, with only the sky for company. The lowercase style adds to the feeling of a private thought, whispered rather than announced.