There's an earlier thread on this; it's one food total for however many stone you're due.
Thanks - I did take a look but didn't find it :/
You're not to be blamed. Regrettably, the poster of that earlier thread posted it in the wrong edition of the game.
For reference's sake, here's that other thread: New Version Roof Ballaster Card (I've submitted a correction request to have that thread moved to this forum; here's hoping that happens.)
In the meantime, a small tip to you for attempting to do due diligence before posting a duplicate thread.