This minimalist birdhouse design is inspired by the strength and simplicity of the equilateral triangular pyramid. Since extrusion-based printing has inherent limitations, the pyramid was used for its printability without support material.

http://www.drsfostersmith.com/pic/article.cfm?aid=2194
using this page as a guide, I added these features to properly accomodate birds: a non-perch entry with an overhang, a covered vent for heat, and a drainage hole at the bottom.

This birdhouse was printed successfully with the default low-quality settings for the MakerBot Replicator2, except that the infill percentage was reduced to 5%. It should be lying on its back with the entry hole facing upwards. No raft or supports are needed but the back edges print much better with a raft. It prints in approximately 5 1/2hrs with a raft and no supports.