By far the most useful item I have ever built has been my 3d Printer.
It is a modified Acrylic Reprap Prusa i3 that I got as a kit and built by hand in high school.
Before I had this 3d printer I used a service to have 3d printed parts shipped to me but over time as I got more into drones and CAD modeling I decided the economical option was to buy a kit.
Projects 