why not go for a simple design from the past, like a more traditional church or one room school house. Then you could easily build on off the side in the future. No need to waste money on design and architects as long as your builder has a very clear view of what you want. A side wall of 9' could easily be added onto and doesn't produce a bunch of waste since you use all the scraps for bracing between studs. If you went with a simple rectangle and you knew how to build a stud wall your congregation could REALLY save some money and build the place yourselves, atleast partly if nothing else. Have you ever heard of Habitat for Humanity? You might have a new church in no time~! Go for a simple oldschool design and everyone will appreciate the beauty and simplicity!!!!