How much of the copy in your designs do you own?

Own it unless there is a content designer, and even then draft it rather than using placeholder text. Copy is interface: labels, button verbs, error text, and empty states do more work than layout in most flows. Write in the user's vocabulary, keep verbs specific (Save changes beats Submit), and test the words with people, because unclear labels are usability failures that look like design problems.

I write it, always, even when there is a content designer, because a mockup full of placeholder text is not a design, it is a layout. And the words change the layout constantly: a button that says 'Publish to all regions' is not the same shape as one that says 'Save'. My source for vocabulary is research transcripts and support tickets, not the internal glossary. If customers call it a job and we call it a work order, we lose every single time we insist on being right. Rules I hold: buttons name the action, so Save changes rather than Submit, and errors say what happened, whose fault it was, and what to do next. When there is a content designer I bring them in at the wireframe stage, not at the end for a polish pass, because half the time they solve a flow problem by removing a screen and rewriting one sentence. On one project our content designer cut a three-step confirmation down to a single well-chosen line and support contacts for that flow dropped noticeably.