Last but not least, build some framing to support the screen. I started from a coffe table frame as a base and a couple wood planks to get the screen up in the air. The exact geometry is dependent on the optics of your projector. The one I borrowed wouldn't focus at close distances so it was necessary to have the light follow a longer path, bouncing off the mirror and back up onto the display. The angle of the display surface matches that of the projector (angle of incidence = angle of reflectance) in order to minimize keystone distortion.