I liked the concept of using a CD as the bottom, inspired by Gyrobot, both for drainage and easy cleaning, plus shortening the time to print. So I modified the Cool Birdhouse to take a CD/DVD for a bottom. See Cool Birdhouse for additional info about the design and instructions. (http://www.thingiverse.com/thing:116693).
Kudos to Gyrobot and the Birdhouse Bauble for inspiring the use of CDs! (http://www.thingiverse.com/thing:105561)
Added a CD as the base - you must print this at actual scale (1:1) for this to work. Otherwise, print the original Cool Birdhouse or use the CD model provided by Gyrobot. Note that there is a bridging challenge at the base, so your printer must be well-tuned. There are a number of bridging and torture test models on Thingiverse to aid you in tuning your settings.
NOTE (7/23/13): I am working on a V3 that eliminates the bridging and should be more printable.