MakerBot is running a birdhouse design challenge, and the first prize is an Eggbot! The challenge runs through July 16, and the designs will be judged on functionality, printability and creativity. There are already quite a few entries on thingiverse, including the Death Star Birdhouse by plainolddave below.
Does it have to be functional?
Many birds require certain volume, size and openings. Not to mention that they should be cleaned out after its yearly use.
The rules are up on the MakerBot blog–you can find the link above.