Building Shading

[Major LEE]

Hep perhaps I find a solution to the problem
control clic on the building layer to load selection
creat new layer under the building one
selct it and fill selection with black
move this layer down and right (about 5 pixel depending on the scale of the map)
copy this layer and move again
repeat the previus step 5 time or more as you want
merge all this shadow layers
apply a gaussian blur to the merged layer
set its tranparency to 50%

[Ascension]

Yep, that's the standard method but most folks just starting out find drop shadows easier despite its flaws.