Combine augmented reality, nano robot swarms and mind-device communication.  So the idea is you first imagine a structure.  This imagined structure is displayed (could be on glasses contact lens etc), augmenting reality.  Using the image you can then improve and change the design.  Could use your hands to manipulate it or just use your thoughts which ever is easier.  The nano robots can then form the imagined structure.  You could then store useful structures for later use and the system could learn to predict and suggest new structures based on your preferences and behavior.

You all knew I am a bit crazy ;).