Concrete roads are exactly like asphalt roads, except they are lighter in color and don't require oil to build. They take only 1 stone, with a variable amount of labour based on how much leveling you need to do. They are placed the same as dirt roads.
Concrete slabs (a road with no directional arrows) placed alone will raise and flatten the terrain square to the highest corner of the square it is placed on, similar to dirt slabs. However, unlike dirt slabs concrete slabs placed next to another concrete slab will flatten the terrain to the same level as the highest concrete slab placed nearby. This means that using a chain of concrete slabs one may lower terrain.
Caution must be taken when lowering high areas, as creating a low tile next to a high tile with a large enough height difference between them will cause the ground to poke through and hide the low tile. This can only be fixed by adjusting the height of the entire area (either making the high area low or vice versa), as there is currently no way to recreate the natural slopes.