Troy, Troy, how does your garden grow?

"This has worked on my roof now for five years," he said. "Once you get the roof established, then it's just a normal garden."

One one side, Wagner has planted spring flowers. Opposite them, he has prepared the soil for vegetables.

"We've tried just about everything. We have radishes here and green beans here," he said.

Another part of the roof is covered with grass. Wayne doesn't even try to mow it. Nature cares of that.

Spring flowers, a spread of vegetables and water-soaking soil -- together, are they too heavy for the roof? Nah, Wagner says.

"There is some engineering you can do that's very inexpensive to be able to handle a load like this," he said. "The house is 110 years old, and I've had no problems. And I'm watching for them."

A green roof may cost two to three times as much to install as regular roofing, but Wagner believes it saves money in the long run since it doesn't have to be replaced every 20 to 30 years.

Green roofs are also eco-friendly since they avoid the use of petroleum-based products. They also help reduce carbon emissions since they naturally make homes cooler in the summer and warmer in the winter.

And green roofs help absorb rainwater.

"The storm systems won't be so overwhelmed," said Wagner.

Wagner was recently featured in People magazine as one of the green roofers in North America. Wagner said he's willing to share the gardening lessons he has learned for free.