My current ongoing project is a large delta printer. Bed size is 510mm and the total height will be 1800mm. The goal is to have a very rigid design so I went with V-slot C-beam 40x80 for the towers and V-slot 20x80 between them. I could not find any suitable corners so I made my own design in Fusion 360 and my oldest son helped me to fabricate them with a CNC-milling machine at his work.
I have all the extrusions and all corners but so far nothing is assembled yet but I have some renderings and a photo.