This is for the pre-93 cars. 

Everyone says, "There's a rubber strap to hold the cargo floor up."  True, there is, but what a pain in the butt to use.  Why not make a simple, automatic catch to hold the floor up?  Saab missed the boat on this one.

bulletCut a small wedge from a piece of wood; most anything solid will do (plywood tends to split)
bulletAttach it to the underside of the package shelf, using two small screws from the top side of the shelf
bulletThe vertical face of the wedge needs to be about 6 1/2" from the rear of the package shelf
bulletThe ramp faces the rear.
bulletPre-drill the holes through the shelf and into the wedge using a small drill bit
bulletnow drill the holes in the package shelf large enough to clear the screws
bulletAttach the wedge with the screws; don't over-tighten the screws.

When the cargo floor is raised until it contacts the wedge, it slides up the ramp, then drops in behind the vertical face; the cargo floor now mercifully stays up and out of your way.  To lower, simply lift the package shelf about an inch and the floor will drop back down to where it normally lives.