Writing a Requiem

I was thinking about starting work on a requiem and I'm just wondering what that involves. Is there a certain set of texts that would need to be included (I've noticed that most requiems contain many of the same texts). Do any of these texts have specific melodies already in place as with a chant? Are there any length parameters I should be aware of? Number of songs? Any other requirements I should be aware of that I didn't ask about specifically? Any help would be greatly appreciated. Thanks!

Wow, a requiem. My favorite thing to start and stop... lol!

Well, to answer your questions the requiem text can easily be found on Wikipedia. The church has made some changes to the mass itself. The Dies Irae is still used but no longer required - at least to my understanding. In the great tradition of Requiem masses composed since the time of Mozart (his Requiem, I consider to be the best Requiem) there has been a great variety of masses. Some composers add to the text secular poetry, other biblical tracts, and other more interesting things - so all bets are pretty much off. Myself, I have been researching ancient latin quotes pertaining to death and life in general and have made movements from these and added them to the requiem format - so anything is possible. Good luck and I hope you post your results!