1, if the number is even, you must put some even numbers on the roof. There are certain requirements in quantity, and more is better, because it is an echo after all, so it is often unlucky to put the singular.
If you put pigeons on the roof, you must pay special attention to the location. You can put them in the four corners of the house, which is also good, or in the middle of the house, that is, the center of the roof.
Solemnly remind: the answer is for reference only, don't be blind and superstitious.