I think you may have asked an un answerable question
Seriously, how would we know about if cops could see them or if they would be hidden?
I will say that growing on a roof can be a little exposed but if you top the plant and make it as bushy as possible then the police might never suspect a thing
i have mine in a garbage can on the roof, gets full sun, i would like to get some mylar in there, but it might get too hot. i made some vent holes. I have 2 story houses nearby, so they cant see my plant now