It's much cheaper and easier to modify an existing truck. Many companies offer a variety of performance suspensions for such vehicles.
Building one from scratch would be a monumental task. You would need a mountain of chassis tubes, welding jigs, tube benders, miter saws, grinders, cut-off wheels and a masters engineering degree to get it right.
If you simply must have a race truck, take a look around and see if anyone is selling one. Sure it may be bent, obsolete and need lots of repair, but it might be easier and better to find one instead of building your own.