There really is no 'original' story. There is a theory that there are only 7 different types of plot in all of literature...what makes them different is the way in which they are told. Rowling's skill lies in imagining a different way to tell the story of a young boy that is raised away from his natural family, suffers abuse, comes into his inheritance and becomes the hero. There are thousands of stories like this throughout history. Don't worry about copying stories - just find a way of telling them differently. If Rowling's stories are guilty of anything, it's the need for tighter editing - the longer books written after her initial success appear to have been allowed to ramble by editors unwilling to say 'No - it would be better this way'...I may be wrong!
What Rowling (and all other writers) should be applauded for is actually getting the story written in the first place. Writers, great and not so great, simply write. That's the hardest part - sitting down and writing. Then they read it, and re-write it. That's the next hardest part. Then they give it to someone else to read in order to find out what else needs to be changed. That's the next hardest part. Then you have to let the public read it and comment on it...actually THAT'S the hardest part!
So my advice to you, Harry Potter fan, is to forget about Harry Potter, find your story, find your 'voice' and write...even if only for the sheer pleasure you get from it yourself.
Are great writers born or are they the product of a good education? I've had a fairly good education and I've been told I have a vivid imagination but no matter how many times I've tried to write even a short book, I find myself copying others. Why can't I think of an original storyline? I seem to be locked into other people's imaginary tales. JK Rowling is a phenomenon. I mean, how do you follow an act like that?