Would used parts even be reliable???
Well, the 1st steps in computer building are determining the use of the computer and your price range.
Determining the use of the computer will help to allow which parts to spend more money. For example, a hardcore gamer would need dual video cards in SLI or Crossfire. But a person who would be recording tv with the computer would need a big hard drive and a not so kick ass video card.
Determining how much you will spend will help you to aim at specific products of interest and good quality. The budget will help you see which parts are the best for how much you are willing to spend on a rig.
Any more help?