The Mirror Theory

So..
Today I watched a video on global warming in my biology class.
I got thinking about all the different ways to get it so the earth would be cooler.
And I came up with a theory, I don't think it would logistically work, well maybe it would?
They talked about how they would like to put millions of these mirrors in space to float around and reflect the suns rays off into space instead at the earth to lower the temperature before it goes up 2 degrees or so which would throw the worls ecosystem off a bit. However here is my theory that I used from that idea..

If there was a way, to get every house and building in the world to put a mirror on their roof. I am talking something like a 5x5 or something fairly large. Then in more open spaces random mirrors in the feilds, and on wind mills, and the maybe even the tops of cars?
Now woud that would reflect a lot of the suns rays back up into the atmosphere and into space? I don't know... Or would it just bounce back down again because of the atmosphere?
I do know those rays would not be obsorbed into all these places right? Where would they go? I would imagine back up. However, I don't know if that wouldn't make a difference since the rays are already in our atmosphere.
This idea would be a lot more cost effective than the mirrors in space for many obvious reasons.
Maybe if somebody comes accross this that knows something about that stuff could comment on it or something.

That is my blog for the day