I'd go with Traction fan's ideas. If you want something that looks realistic, green paper isn't a good route.
Those grass mats will work fine, or you can do what Traction fan suggests. The only thing I'd do differently is to skip the white glue. Paint your surface with dirt-colored paint, then sprinkle the ground foam grass on while it is still wet. You can add more later using the white glue method if you want, and add trees, bushes, and other ground cover as well.
I get a little more finicky with roads. I use strip styrene to make a frame, which I fill with drywall mud -- this has the perfect texture for HO asphalt. Each lane should be about 13 scale feet wide. Level the drywall mud with a scraper made from styrene (for ultimate realism, it should have a slight crown (about 6 scale inches) in the middle. Airbrush it any shade of gray (new asphalt is almost black, it weathers to a very light gray). Add patches of a different shade, make cracks with a Sharpie, paint the pavement markings. You can do a lot to make roads look realistic. Finish up the edges with a little fine ballast to simulate the crushed stone road bed.
Connecticut Valley Railroad -- A Branch of the New York, New Haven, And Hartford
"We don't stop playing because we grow old. We grow old because we stop playing." --George Bernard Shaw