Selling advertisement spaces

Selling advertisement spaces widget. People can upload the proper picture or banner, text, Urland so on and we can set the pricing for each ad space and personally i wouldnt like PPC or anything, just buying the space for limited time i think is best. For the ads we can almost place them anywhere now if we want to but would be much cooler if people can just make them on the site and click and buy the ad space. And there can be many ways to do this and many ideas can come up to peoples minds while reading this, lots of options!