What size pan would make a hat large enough to feed 35? I'm thinking I might should just make a smaller cake and put in on another to get
More servings.

If it's the shape of a top hat, you could stack 8" diameter cakes to equal 6" tall for 36 servings. (You might consider using a cake board in the middle at 3" for ease when cutting.)

If it's another shape, let us know if you need more suggestions.

sorry bout that... I need a graduation hat.

Boy it would be so much easier to make a half sphere cake with a sports ball pan or pyrex bowl and then put it on a bigger cake. Otherwise you'll be doing a lot of carving