I built my own 3D printer based on open hardware RepRap printer Rebelix X2, but improved by my own design customizations. Printer consists of plastic parts made by similar 3D printer (I used 3D printers at Czech Technical University), standard aluminium profiles, stainless steel rods and bunch of nuts and screws.
An easy to setup and easy to use firmware for DIY CNC machines. It supports FDM RepRap 3D printers based on Arduino with RAMPS shield. All this led me to use this firmware on my custom 3D printer.