Ah, white noise to drown out sound disturbance, I've done that too.
(I went as far as going to a place that usually sells hearing aids. They have that goo that is injected in the ear canal and then solidifies in a minute so you get a mould of the ear canal. I had those moulds used to make thingies in which standard earbuds fit. They sell that product to people who want to use earbuds to listen to music. In my case I used the earbuds to play white noise. I still keep those thingies, in case I ever have to share a cabin with someone who snores.)
You describe trying to contact-transfer white noise vibration to a metal roofsheet. I think that is not worth giving it a try. Very unlikely to be succesfull, I think.
What remains is trying to set up sound absorption. There's actually a lot of information available about affordable ways to achieve sound absorption. (A lot of people want to start a youtube channel, and an echo-y room is unpleasant to hear. So you get people filling that need for information on how to absorb sound.)
There is for instance the guy with the channel DIY perks.
He made a video about sound absorption modules that were designed to be effective and affordable.
[Later edit]
Overlooked an earlier video from DIY perks:
The title claims: high performance sound panels for $5
Ironically, because of the way Matt tested: his design is optimal for absorbing sound, not for scattering sound, as is preferable for recording studios. But it's taylor made for you: you want all the absorption you can get. The 5$ price is very optimistic. Matt uses many layers of (old) towels. If you can get your hands on boatloads of old towels: great. But if you need to buy the towels new the cost is going to add up, I think.