There's an article by Jim Brown, one of the most respected people in sound system design, called "Why Churches Buy Three Sound Systems, and How You Can Buy Only One".
You can find it at http://www.audiosystemsgroup.com/3Times.pdf
Read it and learn :-)
The basic story is that the "first" system is designed by the building architect rather than a specialist. Aesthetic finishes are more important than functionality. Components are chosen from catalogues without looking at the whole system. It's not seen as a fundamental part of the building, so corners are cut. It's built to a tight budget.
A couple of years later, when they realise the deficiencies, a "local expert" offers to "improve" things. Often someone that has a band, or a disco, and so "knows about these things". So they build something that's a bit like a big disco...
And then eventually, they get a pro in and do the job properly. An independent acoustic consultant who will specify and design the system, without being tied to any particular supplier. Who has done "church installs" before, and can provide reference sites. Who will manage the tender process and supervise the installation. And who will stake their reputation on "getting it right".