Ask HN: How do you build a self-serve ad network to compete with Google?

Can anyone point me to good resources online to read up about the intricacies/challenges/opportunities of starting an ad network?

Specifically, would love to hear about:

1) How to initially sign up advertisers 2) How to initially sign up publishers 3) Technical challenges

Also, the question is posed in the context of local, self-serve ads (so signing up small local businesses rather than a Toyota or United)