My first big Makey Makey project was to build instruments with my 3rd graders. I first had them build the instrument of their choice. I did get some a keyguitar which was quite exciting. They had to keep in mind to add the conductive components either using copper tape or HVAC aluminum tape which worked better than foil.
Once they completed the instrument, it was time to connect the alligator clips and the Makey Makey. Once Scratch was opened, I showed the students how to make original sounds or use the instrumental choices. Several of the students who were more familiar with Scratch also worked on their avatar to it also responded to the controller inherently on the instrument.
Students loved worked on this project. Some struggled with leaving enough time to program on Scratch because they were swept up in the designing phase.