The RF energy travels at the speed of light.
Even if the signal did bounce off the metal roof it's going to reach the RX at the same time and the same frequency.
What you need to do is go inside that building and see what is running.
I found a building that had a swimming pool seam sealer that had the bar covered with copper.
That bar was actually an antenna for the 440 band and it generated 15,000 watts and that created heat between that bar and the ground plate under the plastic.
If their running something thats in violation of FCC then you can have them shut the equipment down.
I worked with QRM tracking for many years and I'd sure like to see what's in that building.
Go in and le them know what is going on.
Just a suggestion