Richard Greene was reading the Bible one night in 1974 when, he says, God spoke to him. "He would say, 'Richard, there was an Ark, and so shall it be, now build it as your new church'," Greene says.

Two years later the retired pastor from Frostburg, Maryland set to work rebuilding Noah's Ark, to scale, on the edge of an interstate highway.

"I am just like Noah," Greene says. "They're laughing and mocking just like they did Noah. But the flood still came, and Jesus is still coming."

When it is completed, the Frostburg Ark will boast a 1,700-seat auditorium, a Bible college and food and clothing pantries for the homeless.

But almost 40 years and $3m later, how close is the Ark to being finished? The BBC spent the day with Richard Greene to find out more.

Produced by the BBC's Tomos Lewis and Peter Murtaugh