If you use a laptop that you own to do work for the church, it is not a contribution and you cannot claim a deduction for it. There is no deduction for the use of something that you own.
If you donate a laptop to the church, for the church's use, you could claim a deduction for the donation. See the section on "Contributions of Property" in IRS Publication 526. You would need a contemporaneous written acknowledgment from the church and you would have to include Form 8283 in your tax return. See "Noncash Contributions" under "Substantiation Requirements" in Publication 526. The church could then allow you to use its laptop for church business.
