Make a copy of our monument layer and drag it to separate document (create one).



There we have it.



We need this to create a real shadow. OF course I've could painted it but it probably took me some time.

Flip the image and rotate it 180. You will get this.



Drag our flipped image. And here we have it. Now transform the image, using Distort and Skew.



And don't forget the shadow direction.







Fill the layer with color in layer styles menu.



Create an Alpha Channel.