When I think of reasonable cause and police officers, I think of controversial situations like the one in Ferguson, Missouri. Would it be reasonable for an officer to suspect a teenager of wrongdoing because that person was walking down the middle of a street instead of on the sidewalk? I've done the same thing myself late at night, when the traffic on my street is very light. But I'm not a policeman, and I'm not looking at it the same way.
I think it's reasonable cause if someone is doing something unusual and won't respond to a verbal command to stop it. If someone is sitting outside a closed store at 2 in the morning, a reasonable person might want to ask him what he's doing there. I don't know if just standing in front of a building is enough to provide probable cause, however. The officer would have to see something a little more suspicious, I think, like a possible weapon or burglary tools.