How do I value sponsorships, advertising, and marketing by other businesses in my building?
If no one else is selling similar opportunities, it's not likely you'll be able to do it, either. My fear is that you're going to find advertising sales a much tougher business than you suspect. To be successful, you're going to have to have a steady stream of warm contacts available to you and you're going to have to brazenly suggest to people that they should "sponsor this event," "put your ad on a sign right up there," or "take advantage of the captive audience that comes into this place every day."
There is no such thing as advertising that sells itself.
Good luck to you.