I saw this photo on Facebook and thought it might be neat to be able to attach something like this to a bird room. It'd be neat when the weather's good to be able to just open a window and your birds could go in and out as they please and get plenty of sunlight:
The main thing I would worry about though, is making it suitably bird proof. I feel like they'd probably get into chewing the siding of the house and the window frame. :\