Cloud Cuckoo Land: Initial concept art

I created this piece of concept art last term as part of the minor assignment and build up to the final major project. I had a bit of trouble coming up with a concept that I was content with when I was first designing this, and went through several cycles of design processes before making this collage.
I stuck with the idea of the birds carrying the city, as this made logical sense to me in terms of the context of the story: A city run by birds, and its inhabitants wish it to fly; a rational thought to the bird characters of flight would be making it fly themselves, as opposed to creating advanced technology, propellers, etc.

The bottom of the city is created from shapes of amphitheaters, inspired by the original Greek roots of the play. It also creates quite a unique shape, and a base for the city to rest on.
The buildings I wanted to look stacked, built one upon another, mimicking trees and nests.
Overall, I'm happy with this as concept art but will probably look deeper into this aspect of design especially if I'm considering building a part of it; I'll need to know what the streets and details of the city look like.