Can I build my own nas?

So I have some space on my server rack, but not a lot of money lying around.

What I’m trying to achieve is a nas setup for my security camera system. It has 30 cameras, and 4 drives fill up in 3 months. 3X3TB drives.

Looking on eBay for a second hand rack mounted NaS is pretty expensive. Could I build one? From a jbod or something? I’ve got a nice big space in my rack doing nothing.

(I know I could buy bigger drives, but I kinda like the idea of experimenting with something g different) ✌️💛