I dont understand completely your post,
are you building a pc with the hope of selling it to a friend, or have a friend who wants that pc built?
if your starting out its rather/very foolish to spend money on a system that someone 'may' buy, the unit is aging and losing value until its sold, potentially you could lose your entire investment,
much better plan for you,
Make it known in your circles that you build computers, become 'the mate who does computers' to all who know you, school,work, the pub etc
eventually someone will approach you with the magic words, 'Hey I hear you build pc's?'
grill them on what they want the pc for, what its going to be used for and what they are looking to spend on it,
meantime do a lot of research on the different 'classes' of pc and the components involved,
You would no more build a single core onboard gfx machine for online gaming than you would an water-cooled overclocked hexcore with 3way crossfire and masses of lights for your granny who plays farmville,
theres millions before you and millions after you with the same idea, build pc's get paid, I'm one of them same as a lot of people on here,
one thing you could do is post a thread on here occasionally ( dont spam them, you'll get few answers and less help I fear)
asking for advice on for example a £400 workstation rig or a £1500 gaming beast
this is the form to use for that, make it easier for us to help you
http://www.tomshardware.co.uk/forum/261222-13-build-advice
Dont get all excited the first couple of times people ask you to build something btw, its really frustrating when they back out and it leaves you demoralised, but on the plus side, you will (hopefully) have done some research and learned (more valuable than I can stress
)
theres more to say on the subject and I'm sure others will chip in with help/hassle etc
one last thing, as a small builder, you get the money from the client BEFORE you order parts, you cant afford to have parts sitting around for the reason I stated at the top, you'll end up in a room full of worthless bits and skint wondering why the hell you wanted to get into this business lol
Moto