Take it from someone who learned the hard way on building a bike. First take PE's advise, and buy a complete bike unless you are doing it to have a custom bike made just for you. If this is the case I would use pretty much all new parts, as you will be replacing the old parts you use later. I ended up taking almost a year just to get my bike 95% complete because I used old parts when I first built it. I still have junky rims and brakes, but have spent an unbelievable amount of money on it. If I had to due it over I would have bought a complete bike and upgraded it. To sum it up, I have a bike that is worth about 600.00, and probably have 4x's that amount into it.