Just to get technical, the great wall seen from space thing is a myth. It takes super clear conditions to maybe make out a section of the wall with the naked eye from low Earth orbit (not space by the way). It's a bit easier to spot in a good photograph. Once you're on the moon though, you definitely cannot see it let alone any other man-made structures apart from city lights at night.
That's right. The shear length of the great wall (GW) may theoretically render it visible from moon or space, but the width of the GW is just too narrow to be seen at all from that distance.