Help On a Reqiuem Mass

Hey guys :D I'm trying to write a Reqiuem piece at the moment, (partially for my interest and partially cause it's going to be for my exam work thingy I have to do at school). Anywho, at the moment I'm not really sure how I should go about in the piece and I was wondering if you guys would offer some tips, suggestions on what I should do next. Also, I would like to know if I'm on the right track or if I'm making the wrong mistakes since I'm fairly new in composing in this sort of style :D

Introitus idea 5 part 10.mid

Vaguely :P Umm.. Basically I know that a mass is generally sung as a ceremonial thing. The Requiem is similar to a normal mass but it has 2 movement removed and the Dire Irae is added into it. Also I've read somewhere that some Requiems were composed with the intention of being a concert performance rather than a mass for the dead. o-o

Edit: I've been reading sites such as:

http://en.wikipedia.org/wiki/Requiem

http://members.optusnet.com.au/charles57/Requiem/lyrics.htm

http://en.allexperts.com/q/Classical-Music-2272/Requiem-Structure.htm

http://www.windofkeltia.com/requiem/

before I started on composing the Introit, and I've listened to Mozart's, Cherubini's and Brahm's Requiems before hand as to see what a Requiem sounds like. However, I didn't really go into depth with there pieces like analysing etc. into great detail.