Like someone else said- I am getting in late on this. It seems that most of us have seen first hand or heard of situations such as this. As stated, it is a whole different ballgame when you are designing for a room that doesn't exist. At least with a room that already exists, you can take some mechanical and acoustic measurements that will aid you in determining what the room needs. When the room isn't much more than a thought, you have to contend with the never ending stream of design changes that will inevitibly come down the road- pastor wants drywall ceiling instead of acoustic tile- or vise versa! Couple with that the fact that the church's project manager likely has no concept that even a 'minor' change could make a drastic change to the sonic performance of the room and the designed sound system. (Been there, done all of that.)
As the group pointed out- it is always best to identify the requirements up front before selecting any solutions- and this means not just components. If you have the solution in mind before even seeing what the space will look like, you are already blinded to the potential pitfalls of the solution that you chose. Before you can even begin to consider anything else related to this project, you have to fully examine the nuances of the room- without that, you are- as put earlier- shooting in the dark. Sound system engineering is not a "one size fits all" discipline; each design choice brings with it the potential to wreck what would otherwise work well. Just because a particular product worked spectacularly in one instance doesn't mean that it will always work in every application. EAW makes great hardware, for example, but yet, not every (and, perhaps not any) EAW cabinet is appropriate for a given situation.
Likewise, the design has to do more than "look" right. I once evalutated a system in a church where the worship leader installed the system. This room was 30ft wide and 50ft long; he had a pair of 90 X 40 Yamaha cabinets "arrayed" from the ceiling (which was disproportionately low to the room size); needless to say, the results were underwhelming. This person saw other systems where speakers were arrayed together and decided that that is how it is done. Please avoid this kind of thinking.
If you really want to help these folks out- and you would like to learn- perhaps you could find a mentor who would be willing to invest his/her time in walking you and the church through this project. Your physical distance and the fact that you are behind the 8 ball time wise may not make this practical. This project will be a sizable undertaking- a smaller project would defnitely be a less overwhelming place for you to start learning. Read this link too; and copy to the principles involved in the project:
http://www.prosoundweb.com/church/tfw/architect.php A wise person once told me: "Experience is what you get when you don't get what you want."
Regards,
Vinny
