All Saint's Church in Houghton Conquest, a village in Bedfordshire, is currently raising funds via a Facebook page, as well as a church concert and an autumn bazaar this weekend to contribute to the cost.
The Grade-I listed building had approximately 20 tonnes of lead stolen from its roof over a 'prolonged period of time', the police said. An investigation was started earlier this month.
Inspector Nick Masters from Bedfordshire Police said: "Due to the sheer quantity of lead taken, it's unlikely that it happened over a few days.
"It's likely that the people responsible were driving trucks or vans so they could transport scaffolding or ladders in order to access the roof of the church, and may have posed as tradesmen."
According to the church treasurer Joyce Bullock, an architect told the church last week that fixing everything could cost an estimated £400,000.
The church's insurance policy, with the company Ecclesiastical, only covers £15,000 of that - with a maximum of £7,500 for the roof, as they didn't have a roof alarm, and another £7,500 if they want to do internal repairs.
The church has already raised £1,000 via donations and the roof has been temporarily covered with plastic to prevent it getting damaged in bad weather.
Inspector Masters finished his statement: "This is an audacious incident and we're exploring a number of lines of enquiry to find out how this happened.
"Clearly this is unacceptable and we're taking this incredibly seriously."
Stay up to date with the latest news stories from a Christian perspective. Sign up to our daily newsletter and receive more stories like this straight to your inbox every morning.