Here's a site with some decent pics. Most after market roll cages will be like the 8 point. This will do little to help strengthen the flex in a car. It'll just keep the driver safe.

This one will help as it is built in to the frame.

Now this one is what you would need to make the roll cage help save the driver and make the car really stiff to make a difference.

I doubt you want to spend that much on a roll cage to help your suspension so I'd just go with some sway bars and springs and shocks. Tires/wheel size and type does make a difference too.