The biggest thing I’ve built was a production test system for one of the Neuro Muscular Electrical Stimulators I worked on in my first job out of college. I was about the size of an A2 sheet of paper, about 30 cm tall, and weighed about 25 kg.
It has loads of features, inputs and outputs, to test all of the findings of the product.
It was a great project to work on so soon after finishing college, as I gained a lot of knowledge and experience about a wide range of subjects.
The biggest thing I’ve built is a metal shed that we used in my old research lab to shield some sensitive experiments from electromagnetic interference. It was about 2.5m x 2.5m and we had test subjects sit inside it while we recorded electrical signals from their brains.