STATE COLLEGE, CENTRE COUNTY -- Rooftops can seem like a lot of wasted space. But we found a great way to make good use of that space and help the environment too.

At a recent farm show in Central PA, Penn State showed home and business owners a new kind of roof. A green roof.

Instead of shingles, metal or rubber, a green roof uses plants to cover the top of a building.

The environmentally friendly building design has been popular in Europe for decades, and is now catching on here.

At Penn State's main campus for example, the university's Forestry Resources building uses a green roof and so do many other new buildings.

It costs about twice as much to top off a building with a green roof instead of a conventional roof.

But cost isn't everything. Penn state professor of horticulture says a green roof will last three times as long.

And that's not where the benefits end. Professor Robert Berghage said, "The green roof actually acts as a cooling evaporative collar on top of the roof and it's just like a lawn. It's a whole lot nicer to sit on the lawn than it is the asphalt parking lot."

So far, the green rooftop idea has been most popular with universities and government buildings.