Homebrewing - Beer, Mead, Wine, Cider

so my partner is a harry potter fan, from back when What's Her Face wasn't obviously a trashy person. i would just like to preface this by stating that i don't condone the ideas that What's Her Face espouses, we don't buy the merch, we pirated the movies and any of her books in my library had been bought from a used book store which resells donated books.

So in the books, there's a reference to a "butter beer" the kids drink. I'm thinking that this is non-alcoholic as in a ginger beer, or at least not super strong. I wanted to try to make a batch for my partner as a special surprise.

I'm planning on making a batch of this next in the style of an american cream ale with vienna malt as the base, 10% oat and 10% corn flakes, to give it a heavy mouth feel, and adding some vanilla extract and nutmeg for the flavor.

Has anyone here made this before, and if so, how did it go? Any pitfalls to watch out for?