I have also built my own 3D printer, because it is like having your own replicator off Star Trek. The design below were printed using an MCOR Matrix 3D printer that creates prints by using multiple layers of paper.
I ended up building my own 3D printer, a Longboat Prusa Mendel to be precise. This uses fused deposition modelling, basically melting lines of plastic, to build up a 3D model. although it has its limitations it is capable of printing usable objects in Lego plastic. I originally used a Lego turing test to judge my creations, if it could function as a Lego block then it was a good print.