Toggle Terrain Snapping - Blend Building with Terrain

Currently placing walls and foundations in game places them always in a level fashion, often putting them into terrain, with this toggle that would turn that off, allowing you to place level to the terrain. Meaning placing something like a wall around a city would follow the terrain (look at how the great wall of China conforms to the terrain it is on). Additionally, vertical edges would remain aligning strait up at 90 degrees.