Today I came across Building Bytes, who are experimenting with 3D printed bricks that slot together, in a similar fashion to LEGO.
By combining these two projects, plus a bit of solar-powered automation, it should be possible to create a device that takes in desert sand at one end, filters it, sinters it and outputs bricks at the other. Bricks that do not require cement, and are easily stacked into buildings.
Taking it a step further, the GRASP Lab has created quadcopters that can take autonomous components and construct a complex structure. So, sand goes in one end, and buildings come out the other. With little human supervision.