David Finnamore, the elven minstrel of elvenminstrel.com has a very enjoyable set of webpages called Music for Middle Earth.
Middle-earth is mostly modeled on medieval and Renaissance western Europe with a fantastical, mythical twist. Therefore, it makes sense to use European music from before the 17th century in a similar kind of way as a model for the music of Middle-earth. It should not be quite like real Gothic music, as Middle-earth is not quite like real Gothic Europe. But it should be reminiscent of it, and have the same sort of twist.
So how does one go about making music that has a fantastical, Middle-earthly "twist"? I can think of at least four good ways.
(Go to page seven, "The Twist", to find out how to make Middle-earthly music.)