@Professor
The solution would be a Shift-Right click, then Shift-Left click. Find the tile you wish to copy, Shift-Right click it, then go to the tile you wish to replace, and Shift-Left click it.
This is pretty handy for creating the illution of depth in your maps. I hope I wasn't too terrible at explaining that! And I hope it helps!
@Gor
Thank you! I'll add some brick debris on there, just not so big that the characters would trip on them XD
As for your map, I like it! I agree with what Cel said, but that is an amazing grungy map
