If you are building a fast car then this is the one area where it is just not worth it to take any shortcuts. Your brake system is your safety net--if you cannot stop in time, your precious upgraded car and possibly your own life and limb (and the lives of others) may be in trouble. Racing is only safe when you have good equipment, and brakes take top priority on that list.
Since many people have no idea how (disc) brakes work, we will begin with an oversimplified description to put all the parts into perspective. The brake pedal is connected to a piston in the master cylinder, which is airtight and filled with brake fluid. When you press down on the pedal, this moves the piston through the master cylinder, which forces brake fluid into the brake lines. Since fluids do not measureably compress, the four brake lines transmit the pressure to each of the four wheels where they meet the calipers, where there is another piston. This piston is also moved, pushing against the caliper. The caliper then pushes the pads against the rotor, which generates friction that slows the rotor down. Since energy cannot be created nor destroyed, the energy of the cars forward movement (momentum) is converted into thermal (heat) energy. The rotor is connected to the wheel, so the wheel and thus the car slows down. In the process, the brakes heat up tremendously.
Choosing which, if any, brake components to upgrade depends on your driving/racing style, your current setup, and your budget. There are scarce few performance upgrades available for drum brakes and since by their nature disc brakes are more efficient, we will focus on discs here. During heavy braking, up to 80% of the cars weight is transferred to the front wheels which is why on many models the front brakes are disc and the rear, less-important brakes are drum.
Generally, a high performance F-Body brake setup includes strong rotors, carbon-metallic pads, stainless steel braided brake lines, good brake fluid, and strong multi-piston calipers. We will discuss each part in turn.