Additionally, there are many alternatives to freelancer. Before you go build another one, go try out the ones that are out there and see if any of them cover these pain points.
It is not as simple as creating a website. If you want to create a good environment for both coders and buyers you will need lawyers and a good support team. What I'm saying is that you will need to invest a lot of money in something that can be easily crushed (or bought) by the competition.
There are similar (some of them better) alternatives, the problem is that once you have a good history/reputation on one of these sites you can't transfer this to another one. You start from zero.
I kinda dig oDesk. I got many decent clients off it. I was shooting for small, very short term projects - the kind that can be done within a day - so YMMV.
This very site's monthly freelancer thread is also worth checking out. I got a few decent leads out of it.