h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

its arguable that kraftwerk build their own instruments . rather they took standard devices and mounted them in thier own
cabinets for conveniance. they played on factory equipment such as Moog and Oberheim. And last but certainly not least: they used acoustic instruments in their early days

Well, they did build some of their early electronic drums - They in fact used wired-up metal knitting needles to close a circuit when striking a metal "pad" to send a trigger. They didn't build their own synths, per se, but they did build some of their own gear. They also have worked closely with Doepfer over the years to design synths for their performances. Much of Doepfer's product line was prototyped in conjunction with KW.