Yeah you are at the wrong place. Tom's Hardware is a technology news and information website and these forums are mostly to help people with computer problems. There are other sections like here in the Deals area where people can buy and sell computers and computer parts but Tom's does not offer any services like building systems. Without knowing where you are I can't really point you in the right direction either.
Now we can use your budget to tell you the best parts to buy for your money. If that's what your intentions were then please make a new post in the Systems section of the forums and follow the list here: