When searching for similar sentences, it is a good idea to first try the exact phrase you're looking for, without modifying it. If I do a Google search for "next room over" (instead of "next over"), it comes up with quite a number of examples. The problem is that you modified the phrase in a way that changes it into something people don't say.
In this case, "over" is added to emphasize that something is physically neighboring or right next to something else. "next room" could mean the next room in a sequence, etc (for example, if people were going from room to room, the "next room" might be the next one that they go to, even if that's not physically right next door), but "next room over" strongly implies that the room in question is physically side-by-side with the current one (probably sharing a wall).
This use of "over" with "next" doesn't just apply to rooms. It can also be used with all kinds of other things to imply the same thing (that they're physically side-by-side), but it's always in the form "next (noun) over", never "next over".