How much storage an individual user uses on a Mac

Hi,

I own a MacBook Air (13-inch, Early 2014) that has 128GB. Now, I got given this MacBook by my uncle with little warning, but he told me not to delete anything on his user account. Afraid of accidentally messing around with his files, I made my own account and have used it ever since. It was fine, but I downloaded a lot of stuff without really checking the storage of the MacBook and found myself in the ever-so-dangerous <1GB territory, so I deleted a ton of files and applications in order to save myself, now with 25GB.

25GB is the most storage I can remember having, but -- as stated earlier -- I never checked the storage, which was a horrible mistake. My worry is that my uncle's stuff is taking up the majority of the MacBook, which seems like a no-brainer, but I wonder if there's any way to see how much storage each user is taking (say, something that can go, "User X is using 70GB, and User Y is using 30GB").

Are there any applications or hidden features on a Mac that can possibly do this?

Thanks,

Josh