I could be mistaken, but I think Sears had a line of roof mounted cargo carriers called X-Cargo, like AFI292 mentioned. Ya might see what they have at their store... You might also check at a larger Ford dealer's parts department. Some of them have a pretty extensive line of accessories.
It used to be pretty easy to mount a roof rack on a car when they had rain gutters, but with the new aerodynamic styling, it gets more difficult.
If you guys are talking about those "turtle shell" things, all they do is have straps that hook inside the roof where your door closes. They make all sorts of shapes of hooks for different cars. They don't hook on the doors themselves, since you would not be able to open the doors, they just use the inside door jamb. If you understand let me know. LOL.
Yakima, Thule, Saris are a few brands. I personally own a Saris, Thules are good, Yakima are probably the most common, but you pay for the name brand. Each has a website, and most are available at your local bikeshop.