There is a printer that I built some time ago. It’s modified Prusa i3 with bigger print area. It’s 300x300x200mm instead of 200x200x200mm. It may sound like nothing difficult, but it wasn’t so simple ;)
Enlarging frame was quite easy (even that I mistaken in one place and had to add some plastic parts afterwards). The biggest problem was the heated bed. 1,5 times longer and wider it' has more than 2 times bigger area. I didn’t found PCB heater that big so I decided to use big 50W resistors to heat bed. This made bed quite heavy so I had to use bigger stepper motor on Y axis. There was also some problems with overheating stepper drivers but one fan solved them.
Bed that big also requires extra power. I decided to use two separate power supplies, 24V 15A just for bed and 12V 20A for everything else. That works fine.
As you see on the photos, wiring looks just like a plate of spaghetti. It’s pissing me off, and I’m working now on my own version of RAMPS board with some better wiring system.