objects have a position which is usually expressed with three values - x, y and z, or east/west, north/south and up/down.
the command to get an object's location is
_position = getpos object_name
the object's location will be stored in _position.
to set an object's location, the command is
object_name setpos [x, y, z]
so. to make this work in your situation, place the searchlight in the editor as close to where you want it on the building as possible, and give the searchlight a name in its 'name' box. in its init box type
this setpos [getpos this select 0, getpos this select 1, 15]
which will put the searchlight 15 metres in the air at its present position. you may need to adjust the 15 to be the right height of the building in question.