Ours is a combination of a shed roof that attaches to the side of the house (attached at about 5 ft high, slopes to 4 ft something at the front edge) with diagonal bike parking beneath, constructed with a couple of 4x4s along the back and triangles coming out diagonally to hold the back tires in place. It runs the entire inside-the-fence length of the house, and is made from clear ridged roofing panels. In addition to um, "a lot" of bikes under there, it also keeps the garbage and recycling bins covered and in one place.
The working theory is that it should be easier (or at least no harder) to pull out a bike and hop on it then to jump in the car. Seems to be working. (The nice bikes are locked, but merely enough to make it inconvenient to steal them for a joyride -- cutting the cables or 4x4s would be no huge deal.)