I have this story idea called "Evening Mass"-it's about a young, newly appointed preist who is stuck with leading the evening mass at a local basillica.

On his second night he spots this woman sitting in the very back of the church. He forgets his place in prayer because it's as if the woman is looking into his very thoughts.(it turns out she's a vampire)

she only shows up at night(obviously) and after about a week the woman approaches the young preist in the church parking lot with a single question "will you tell God something for me, a sinner"

anyway, one thing leads to another and the preist is turned into a vampire. He refuses to kill anyone and ends up killing himself by walking out into the sun.

Would this be considered Christian horror? Maybe not very good Christian horror but Christian horror none the less

If it has bible phrases in it I would consider it Christian. Otherwise just a bad book. :-)

I think it sounds like a cool idea for a book!   To be "Christian" horror, though, it would need to more in line with Christain theology on redemption and salvation - having the main character kill himself would be decidedly un-Christian. 

But if he were to merely endure and try to force himself to act "human" despite his inner nature, it could be an interesting analogy to how some Christian homosexuals try to reconcile their religion with their inner selves.  (Sort of the way I've heard that the"Twilight" can be seen as an analogy for the abstinence movement).

That plot is very similar to F Paul Wilson's Midnight Mass.  In that book, there is a vampire epidemic and more than one priest gets turned into vampires and some try to fight the urge.

What about Ted Dekker? His are of good and evil..and great reads!

I've read Ted Dekker too and he is pretty good. I also have a Frank Peretti book, but have not read it yet.  Those are both christian horror authors.  I think you also need to be careful about how you write- like no profanity.  I'm not a big vampire fan.   I think your ending sounds just like the movie 30 days of night.  That is the same thing the main character did in that movie.