When you send fakes, if you target Tournament Square, Workshop, barracks, stable, great barracks, great stable, or armoury, you can find out good information about a village. For example, I sent some fakes to Rolly, and I discovered a Great Barracks:

http://travian-reports.net/us/raport.php?id=ae9a088f8

Note that the troops don't have to live to tell you that such-and-such was not damaged. This technique was frequently used in earlier versions of Travian to discover the levels of buildings, but the format of reports was changed from "Great Barracks damaged from level 17 to level 17" to "Great Barracks was not damaged" so that you can no longer discover the levels of key buildings like Tournament Square or cropfields.

Another note is that you will not find out this report if the village traps your fakes.

nice one buddy,,,
but is it that we should set the target to great barracks,,,
while launching the fake,,?????????????

Yes. Set the target to whichever you want to find, and it will tell you if that building is there. But you have to remember what you set, or you'll never know. : )