Well, all of those solutions work well, but if you already have roof bars and baulk at paying $300 for a few bits of pressed steel and aluminum it's very easy to make your own wooden rack.

Just buy an axle clamp, screw it to a length of wood and use some axle U-bolts to secure the wood to the roof bars. Mine cost £30 in parts, took 4 or so hours to design, build and paint and is still working nicely after 4 years. Milage suffers though, and if you drive at 100mph+ with 2 single bikes plus a tandem on top then the tank drains quickly.

Yes you have to lift the bike onto the car, but with practice this is easy as long as you focus on getting the rear wheel safely on the rack, then focus on dropping the forks into the clamp.