If I were trying to think of a new website to build (which I tend to do several times a week), another freelance website would be very, very low on my list of good ideas. Not that the idea itself is bad, it's just that this subject has been done to death. If you want to know what type of websites NOT to build, just have a look at Ebay sometime, in the websites for sale section. Anything you see there is best to be avoided.