Hm, ok. That's changed a bit since I last looked, I think.
Basically, you have to pass the written test, which is the $150. That's a bit more in depth than you might expect, though.
If you've already got your license and are current, it's a free add-on, pretty much.
So not quite as bad as I'd thought it was. Still, not trivial.
Personal use, pretty much, you just need to register it (as far as I know, I'm not actively operating unmanned vehicles so don't use me as a reference here). Commercial use is where the FAA cares.
I believe you also need a handheld aviation radio, or at the very least should have one to monitor local traffic.
https://www.faa.gov/uas/faqs/ has a bunch of information.
https://www.faa.gov/uas/getting_started/fly_for_work_business/You'd need waivers to fly "over people," and given the FAA's approach to regulation, if you're flying over a building, you're probably flying "over people" by their standards.