The section I would write on amateur radar would specifically be in terms of a passive radar. A passive radar requires no approval from the FCC and has the benefit of versatility, as it's typically built off two SDRs. I haven't done much research in amateur active radar, but it seems those types of projects at best detect a 1 m^2 RCS target at <50m. A passive radar can detect a 100 m^2 RCS target flying at low altitude 20km away (webm). As for picking up a drone: you might have luck with a quadcopter, but if you're talking about fixed wing UAVs like the MQ-1 then it depends on how effective their RCS reduction is.
If webm related are generally flying at 20k ft, then a 100 m^2 target at 50k feet would show up at 13km, and a 5 m^2 target would only pop up at 0.650km. If you're interested in locating military fixed wing drones, then you'd have better luck researching your local band plan and finding the bands the UAVs will likely use to transmit video & telemetry. I don't know as much about US UAVs, but I know the Orlan-10 flights have to have at least one, if not all, UAV transmit information back to a ground station when operating. I do remember a story from several years ago mentioning that the MQ-1/9 transmit unencrypted video omnidirectionally, but that's been "fixed"- probably either omnidirectional encrypted or directional now. Judging from the recent story of Iran intercepting MQ-1 video, I'd guess it's the former.