Its going to be hard to make money like that. Compare yourself to say Dell, HP, Alienware type companies. Realize that you don't offer any warranty, tech support or even some kind of certification that you know what your doing. Nor do you have any advertising or reputation.
If you want to go this route, build to order PC's. Ask around friends, family, school-mates or other people in your local area if they need a computer built. That way you offer a custom, personalized service and you are somewhat known to the people who are buying. Stress the fact you can custom build a machine to suit their purposes, which they wont get from going to Dell or whoever. Build them the rig and throw $100-150 on top of the price as a builders fee.