to tell you the truth your not going to make money doing this. First of all who is going to want to buy a computer from a single person with no warranty. People would rather have a warranty and computers made by a buisness even on ebay people sell custom computers made by their company. The way to make money doing this is by getting the cheapest parts you can get and using them. Your not going to make much money if you build a nice pc and put it on ebay probably around the same it costs you to build. Good luck if you try but if its just you doing it you wont really stand a chance.
INTEL CORE 2 DUO E6420
ASUS P5N-E SLI nVIDIA nFORCE 650 SLI
CRUCIAL BALLISTIX 2GB 667MHZ 3-3-3-12
RADEON X1950 PRO