Do not use patch meshes for terrain, they are not suited for it. Either use the method explained by Sockter and used by Dasprid, or use the old method of 'trisoup', just create a grid of equally sized square brushes and clip em all diagonally, leaving you with a fancy grid of triangular shaped brushes. Now you select verts and start pulling them in any direction. While the trisoup method is easier, the method used by Socker has a better endresult, certainly when it comes to r_speeds. Whatever method you use, be sure to use a phong-shading-shader to make the terrain appear more smooth, as shown in Ancient Remains and Sokolov's Space.