Tonight at IAAC, Enrico Dini, an italian civil engineer, gave us a lecture explaining how he developed his idea of printing houses. Enrico showed some images about his first attemps, and then he explained how he figured out the whole process. Finally a debate took place and several students could ask and comment some of the issues that the lecture rise up. 3D Printing applied to a large scale is a new Construction Science. The pages of this book are all blank and need to be written from scratch. Building through 3D Printing means : a new machine; but, what embodiment? how big? How tall? How fast? How accurate? A new process using new materials or old materials in a new way, but what binders? what fibers? what additives? What methods to achieve structural performance? A new Building technique : just one? Maybe many? Which should be adopted first? But the biggest question is : what should be done with the 3D printer, a new tool for a new architectural language? what to print? what to sell? How to design? Freedom of Creation: Is it really true? What are the constraints? How to solve practical matters? Printing on site or off site? Enrico Dini has spent the past seven years facing hundreds of questions and answering roughly just a few of them. During his lecture Enrico will explain the story of a challenging, painful, exciting invention process, still on going and full of surprises, mistakes and discoveries. He found his way: mimicking nature.