Well, if you want an AM station as a hobby, and you can afford the royalty fees, power bills, TAXES, etc... I say "Knock yourself out".
However, if you're actually expecting your station to make enough money to survive, it's going to be nearly impossible with rock & roll. Why? The audio quality. Young people simply WON'T listen to it.... especially when they have MULTIPLE stations on FM... or their own MP3's.
For an AM station to survive, nowadays, it has to fulfill a need in the area it covers: Specifically, a need that no other local station is meeting. One of those needs is broadcasting local high school sporting events. If your station is in a town where there's a lot of interest in the local HS team, then you would do well to secure rights to carry their games. Most likely, you will also be able to find talented and capable STUDENTS to help you with your station.

Get enough students on board, and their parents will listen. Have a local presence and involvement... talk about the stuff in your station's area, local restaurants, events, etc... you'll do well.
Play head-banging music? You'll be mostly ignored. Now, like I said, if you have money to burn, and are just looking for a great hobby... go for it!

Have fun!
PS: I'm not being sarcastic.
