Is this space for sale?

Here's a quick question.

Advertising space.

What's the best way to sell ad space to businesses and advertisers. I was reading about this idea from J.F. Straw. It recommended that you set up an advertising board and sell I think 100 spaces.

He even had a nice idea about putting the boards up on buildings that had places for rent and had a lot of foot traffic. The idea was that you would negotiate a deal to rent the window space. Not the floor space. The owner would at least be receiving some cashflow until the floor space was rented.

The issue though is filling up the board with advertisers.

Any ideas or suggestions would be helpful.

Keir