There are two types of films - one made by the big-time producers, the other is low budget stuff made by some producers who make films for the heck of it, they complete their films for small amounts, sell it at low costs with almost no publicity.
But things such as 'Harry Potter', all I can do is shape my character, seek the director's approval on that, and basically take it from there. Professor Flitwick in 'Harry Potter', I kind of defined how I saw him from reading the book, and luckily that matched up with the director's vision.
Americans are from Mars, Europeans are from Venus: they agree on little and understand each other less and less.