In its simplest form, a sound reinforcement system is a just a series of components that amplifies sounds louder and may distribute that louder sound to a larger or more distant audience.
At a minimum, a design should include the type of speakers, the placement of those speakers, and coverage of those speakers in that space.
Within churches, I think this is where the problem exists, when they think about sound reinforcement systems. Many often come to think, "Well, I can't hear here, so let's just put some speakers in this spot to fill in the lack of volume." In truth, there is a lot more involved than just putting speakers in random locations. This is where a trusted experienced integration company would come into play.
Integrators should be a church's resource to help accomplish this task. A good integrator should have the correct assets to create documentation that show a design layout for that room. At a minimum, this design should include the type of speakers, the placement of those speakers, and coverage of those speakers in that space.
The type of speakers is important in several different aspects. First, this will impact cost, and this is something that usually weighs heavily on a budget. This will also affect the placement and coverage. It is usually true that the more expensive the speaker, the better it tends to be, even if it not always the case. This selection will also affect the sound quality of what will be heard throughout the space. What should also be considered when selecting speakers for your worship space, is knowing what they will be used for. Is this type of church really worship driven, and therefore needs to have a really musical system, or is this type of church that is more spoken word driven? This can really help decide the overall selection and design of the space.
The placement of speakers is key to the overall design and the integrator should give you drawings that show placement and coverage. They should be able to create your space in a 3D environment and show the correct placement of your selected speakers. This should include height, angle, number of speakers, and locations. This will affect the coverage of the room. The integrator should also show you vertical and horizontal coverage throughout the space. This coverage should include the number of decibels throughout the space. This means that they should be able to tell you, for example, that at this seating area it should be able to get this loud. You want to be able to see no higher than plus or minus 1 to 2 decibels, from both left and right to front to back. This documentation should show an even coverage throughout the space.
My last thought would be, ensure that the integrator now knows how to integrate that system. It looks all good on paper, but can they pull off the job?
It would be the church's responsibility to research the integrator’s track record. The church should ask the integrator for references of jobs they have done in the past, and the church should call those places and ask questions, such as relating to the ease of the installation, and how they handled any issues that cropped up.
If possible, even visiting those locations where a prospective integrator had completed a project would be pertinent, to see how the completed project turned out. Ask to see if you can walk the space to check out how the coverage is in the room. Can you hear evenly throughout the space, does it even sound good, etc…
I would even recommend going to the back of the equipment racks and see how work associated with that part of the install looks. This will show you if the integrator takes time and pride in their work. Are things labeled, is gear easily accessible, is it clean and dressed, etc… This says a lot about the integrator and cleanliness is close to Godliness.