Is your current church DEAD? Do you find your local fellowship seems to have very little love for each other or is not very enthusiastic? First try to find an existing group that suits your needs. If none exists then it may be time to start a new church. Does your fellowship have local leadership do just about everything in regard to serving? The involvement of ALL those who are converted is vital to the spiritual health of an individual and a group. If it looks like your local worship group will not soon be changing how it operates then it may be time to begin something fresh.
Are religious politics greatly decreasing your group's effectiveness? Christian leaders who are more concerned about their position and pet programs often resist God's spirit. They may even try to STOP efforts by some to play a more active role in the local church. If you are in such a group it might be time for a change. Is SIN openly practiced by some in the fellowship? Those Christians who habitually sin should not be allowed to come to worship services until they repent (1Corinthians 5:1 - 7). If such sins are allowed to exist unchallenged, it is likely time to start something new.
Do you have significant doctrinal differences with other church members? Disagreements can be worked with if the local group allows open discussions regarding its teachings and practices. If, however, leadership is unwilling to take seriously your concerns, you may be more comfortable elsewhere.
Do you feel that God is leading you to serve others in a unique way? Your ideas may be worth pursuing. If, however, you find your congregation less than enthusiastic (if not downright hostile) to your sincere plans, it might be time for the freedom a new church can bring.
Here are some BAD reasons to start a church. Do you think you know just about everything important the Bible teaches and feel compelled to "bless" others with this insight? Do you believe God has given you some special prophetic insight that has to be heard by everyone? It is a bad idea to begin a new group for the sole purpose of giving you an outlet in which to express your 'superior' gifts! Such self-centered desires can easily lead to vanity (the devil's chief sin) and a host of problems in the future.
Are you frustrated by not being recognized for your efforts in support of the congregation? True Christians serve because that is what God wants them to do, not because they can earn the accolades and respect of others. Creating a new assembly just so that your talents will finally be duly appreciated is asking for a great deal of trouble.
A desire to serve God and the brethren in love and a willingness to work hard are the foundation stones on which to start a church. While knowledge of the Bible is important, it is not the critical asset in creating a new group. New congregations have a much easier time taking shape when people or families of the same mind all pitch in to do whatever work is needed.