Generally, you can deduct gifts to charity of:
*Items (at present fair market value)
*Money (cash, checks, etc.)
*Mileage you drive providing service to the charity
*Money you spend out of pocket to support the charity and its' purposes.
You can't deduct the value of your time. Documentation requirements for each type of donation vary, ask more if you are confused.
However, I want to add some additional comments about "church we helped start." First, it's common for new organizations to not have the reporting and documentation requirements in hand. The IRS has lots of information for charities including how to report gifts and issue receipts and acknowledgments.
Second and more critically, the IRS has rules against self-dealing that can come into play when you are closely connected to the charity. To invent an obvious example, if you as a private citizen, donate your car to the charity, which you as an officer of the charity then continue to drive, that's probably illegal. Or, if you donated $1000 to the charity, which then reimburses you $1000 for your services, that is probably also illegal. Or if you donate $1000 to the charity, which turns around and hires your law firm to provide incorporation papers for $1000, that could also be illegal self-dealing.
In a similar note, if you make a gift and you retain control over how that gift is spent, it may not be tax deductible any more. For example, if you donate $10,000 on condition that it can only be used to hire your favorite candidate for the assistant pastor job, that may not be illegal self-dealing (unless the AP is also a family member) but it's probably not deductible either. But if you donate money for the AP salary and someone else makes the hiring decision, that's perfectly deductible.
To avoid the appearance of self-dealing, any receipts and acknowledgment letters you get for donations or paying out of pocket expenses should be signed by a different officer of the charity, even if you are normally the person who would sign such letters for other donors. Decisions about how to spend money you donate should be made by someone other than you, and if you are on the finance board, recuse yourself from the vote. Take other common sense precautions to avoid the appearance of a conflict of interest or self-dealing.
The self-dealing and control rules apply at any charity or church, but I think they are more likely to be a concern when you are a founder or a senior office of the organization.
