Well, my first thing is I like the whole magic to create not magic to destroy thing. I think you can create an interesting magic system just using that as a base concept. If that's the case, are there other forms of supernatural what-have you that is basically the flip side of the coin? I'm big on balanced forced and all of that, but I think if you're going to go with this using magic to create thing you're going to need to fully explore what all that means and set up some rules for it. What all do you want magic to be able to accomplish. What do you mean by create? Can you use spellcraft to completely build something from nothing but energy and will then? Would creating a fire column like we see Harry do fall under "create" as you're "creating" fire, even though the intent of the fire might be to destroy?
I think that's some food for thought in that department. As far as adding spice and so such...I generally look at a lot of mythology and metaphysics when I'm figuring out the nuts and bolts of magic. I'm also a neopagan, though, so I have a lot of references for energy channeling and all of that just kind of laying around my apartment. You could draw from things like the old Greek version of the elements and how everything is made from Earth, Fire, Wind, Water (and Spirit, too possibly) and find a way to incorporate that. There are a lot of sources, but that's somewhere to start with that.
And as far as the clones thing...speaking as an English major, really everything's been done before. It's not a good idea to blatantly rip other people off, but at least when I do stuff like this I usually start with a "Hm. I think I'd like my magic to work kind of like it does in this book, but I want to also work in this idea. And I really don't like this bit, or it doesn't work for what I want to do, so I'm going to get rid of that...and replace it with this...and then I like this idea from this other thing I read, so maybe I can do something like that..." Eventually you get to a point where you can still see influences from other sources, but you can't look at one specific source and go "You totally copied that!" *shrug* My advice there would be to give it time to cook in your own head. You'll put your own spin on everything without even realizing you're doing it, most likely.
I hope this helps some.