Imagine you did not have NPM, how would you solve the problem?
Now the question becomes how do you use NPM to automate the solution to the problem.
The reason I phrase it like this is that every environment is different -- e.g. I have a shopping street with every other business offering free WiFi running along the edge of campus. Some of our buildings are very tall with Line of Sight into other apartment blocks. So if I simply looked at the SSID's being detected I have over 1000 rogue APs on the network.
If you have rogue AP acting as repeaters then you can see if there are multiple MAC on a switch port where you only expect 1
If you have rogue AP acting as routers (e.g. most home networking devices) then things are harder as you only have one IP and MAC on the port.
(tools like Aruba Airwave, and Ekahau HeatMapper might be the better solution)
/RjL