Just released from the ESA is a video outlining exactly how we can construct 3D printed bases on the moon. While there are still some challenges to be overcome, many have been met with solutions, like how to provide housing for moon bases. The ESA has a plan for delivering an inflatable scaffolding to the moon and then employing 3D printing robots to create a regolith shield over the structure. The big question still remaining is the materials to use in 3D printing, and whether they should transport binding agents to the moon or attempt to make them there through heating up regolith with solar power. The video, as well as further details on the two possible ways they look to accomplished the printing of a moon base can be found here: http://3dprint.com/23517/esa-3d-printing-on-mood/

Below is an image of a 3D Printed moon base concept: