The simple answer is nothing and everything.
I am sure you have seen massive churches that have very low attendance, relative to their size. I am also sure you have seen a small church bursting at the seams with people. As with most things in life, shall we say, the answer is also complicated.
Holy Spirit-filled ministry in any building brings growth, but I also believe that great Spirit-filled ministry results in great things that permeate throughout the entire ministry, including the facility.
So what can you do with your facility to help encourage attendance?
1.) People come to church for an experience.
This experience is both spiritual and social.
I worked with a church who had an amazing piece of local artwork that you encountered as you walked in the front door. It was a beautiful representation of Christ made with tiny pieces of colored glass.
It was such a thing of beauty that it caused you to pause and take it in. It also became a great discussion starter for anyone new to the church. As they would see the art piece and stop to gaze at, a well-positioned greeter would chime in at the right time say how beautiful it was and how it was done by a local artist.
For those that attend or visit this church they have an experience that immediately points them to Christ and at the same time offers an opportunity for social engagement. What in your facility brings a social or spiritual experience?
2.) People come to connect and fellowship.
One of my favorite things to do before a worship service starts is to hang out in the lobby and just observe what happens out there. It's great to watch old friends connect, to see people hug those who are hurting and to watch the joy the expressed and people connect.
Do you have a place that allows this connection to happen? Do you encourage it by placing appropriate furniture and fixtures around to serve as anchors for people to connect?
3.) People come to find meaning.
One of the reason people come to church is to make sense out of this crazy life. As mentioned above artwork can be a great way to for people to see things in a different way. Sometimes art can be that catalyst that helps one find meaning.
Something as simple as having a place for people to bring goods and items to drop off to go help the needy is another way for people to connect and find meaning.
4.) People come to seek respite from a noisy world.
Today we are all bombarded with so many messages, many of them conflict with our Christian walk. People who come on Sunday are wanting to take a deep breath, refocus and if only for a brief period of time get some separation from the noise.
In your facility are there areas where one can "escape" and get alone with God? Do you have separate prayer areas? Seating areas that are in some out of the way places? Ultimately it is the individual's responsibility to detach from the noise. However, some simple things in your facility can help facilitate in that endeavor.
I really like it when there is a separate "quiet room" This could be a classroom that is converted into a prayer room. Use soft lighting and comfortable furniture and a door that closes to create a living room type of atmosphere and separation.
5.) People come to seek comfort
One of the great comforts we have as Christians is having others pray for us. The prayer room that is mentioned above is perfect for this. Make sure your congregation is aware of this room and encourage them to use it.
By providing appropriate space, atmosphere and experience your facility can help provide ways for people to connect and be ministered to and thus encourage people to keep coming back on a regular basis and to invite others.