I just want to add some roads to my terrain, can I somehow texture the terrain or do I need to add road objects onto it?
You can easily paint on roads the same way you paint grass textures.
If you want something oriented on the road, like while lines, then you need to use a model. But textures work fine for bricks, gravel, dirt… . If you look at most MMO’s, the roads in them are just painted textures – looking closely you’ll see the pattern on the road doesn’t turn when the road does.
You could use the Road and Path Tool by Six Times Nothing, or model your roads in Blender. I usually make a track in a modeling program as one object by extruding a plane and rotating where it should go. If your going for a city with blocks, and buildings, I suggest a low poly road made in a modeling program.
Maybe RoadArchitect would be useful? It automatically adjusts terrain height and allows deep customization of the road network. Roads are placed simply by clicking on the terrain. It’s free and open source.
I am one of the main developers on it.