Jon Richards, 69, originally told his wife Muriel, 68, that he was building a shed. But he said "the game was up" when gothic stained glass windows arrived to be fitted.
The couple, from Studley in Warwickshire, travelled the country to find artefacts to put inside the chapel. A bronze statue of Jesus on the cross was found at a scrapyard in Bristol, and a tapestry featuring the Last Supper was found at a market in Spain.
The couple rescued full-length pews from a church in Herefordshire and put them into the chapel, meaning it can seat 12 people. Mr and Mrs Richards have allowed the local church to use the chapel occasionally for services.
It cost Mr Richards £10,000 in all to build the small church. It's called Chapel of the Crosses, after an Easter procession that goes through Studley every year, when the community puts up three crosses on the hill.
Chapel of the Crosses is a replica of the couple's local church, in the nearby hamlet Mappleborough Green.
Mr Richards told Premier's News Hour: "It was a surprise for my wife. It just seemed a nice thing to do for her, a place for her to go for peace, quiet, worship, and that's the reason I did it.
"I didn't expect it to be such a success with people outside.
"It looks like an ordinary church but a very scaled-down [version], pews either side and it's got the altar and the altar rail and the saddle of seats either side of the altar.