When I first saw a image of a mirro like this, my only thought was: I want this!
Hence I spend around 50€ as well as an old tablet and build a Smart Mirror myself.
The mirror face is a acrylic glass pane with a "one way mirror foil" (this) adhered to it. On the back is a black foil with a recess for the tablet. A one way mirror out of glas was too expensive for me and too difficult to handle, in addition I was not very sure about the transmission properties of the glas one. My solution unfortunatly has the disadvantage that the surface is not perfect (it is IMPOSSIBLE) to attach the foil in a smooth way.
On the back there are a few wooden sticks to stabilize the mirror and to put it on the wall. The frame is out of wood as well.
The tablet (Nexus 7 2012) runs under Ubuntu, since it is easier to administrate remotely via SSH than Android. It permanently displays a website with a white font and a black background. I mainly used code from my home automation system for that.
It displays weather, time, departures at the nearby tram station as well as the newest tweet of a selected user.