Not only can home-built 4x4 bumpers look cooler and cost less than pre-made units, they give the truck owner the option to mount a winch, headlights and brush-guards in whatever way he chooses. Bumpers can be a fun weekend project for fabrication-savvy off-roaders or a weeks-long practice in engineering and aesthetics.
Before getting to work, you'll first have to determine exactly what your needs are. Bumpers come in two basic varieties: formed steel plate and welded tube. Formed steel plate systems are made by welding together flat sections of steel plate, and are inherently more versatile than welded tube bumpers. Although welded tube bumpers (which are made by welding together sections of rectangular and/or round steel tubing) aren't as pretty as plate steel bumpers, they're just as strong or stronger and are generally much easier to build.
In general, you'll want to keep you bumper at least the distance from the body as the stock bumper, but you can go further out if need be. The more distance you can put between the bumper and the truck body, the more room it will have to move if you hit something. Instead of taking the easy route and just making a perfectly straight bumper, giving the bumper a slight backward angle (of at least 20 degrees) on both sides of the grille not only looks better but can help to keep you from getting hung up on trees and obstacles. If your state laws regulate a truck's allowable lift solely by bumper height, this is your golden opportunity to elongate the bottom to give you a few extra inches of perfectly legal lift.
The simplest and most foolproof method for bumper building is to leave the original bumper supports attached to the truck (or make new ones from 1/4 inch plate steel) and tack-weld the bumper together while it's mounted directly to the truck. Aside from keeping both sides symmetrical, the only thing that need concern you is how the bumper looks and how strong it is. Start from the center and work outward. Start by welding the tubular or 3/16-inch plate steel to the bumper brackets. Build out to either side, tacking on the end pieces at whatever angle suits your application. If you're building a plate-steel bumper, frame in the top and bottom with a solid piece of 3/16-inch plate steel.
At this point, you can frame in a front grille guard from either 2-inch square/rectangular tubing or 3/16-inch plate. You can use 1/2-inch-outside-diameter square or round stock to build a set of headlight brush guards, and cover them with steel diamond mesh. Once you have all your accessory holes drilled and everything tacked together, remove the bumper and finish-weld it all together. Instead of paint, you might want to consider a textured truck-bed coating; such coatings will endure the scrapes and bangs you're likely to encounter off road, and will do a good job of covering up any blemishes in the welding or metal.
