Of course Freeman Dyson came up with the idea of a space living organism many years ago-
the Dyson Tree
http://en.wikipedia.org/wiki/Dyson_tree
a fictional take on this concept:
http://www.orionsarm.com/civ/Dyson_Trees.html
my picture of a dyson tree...
click for larger image
the most important aspect of a Dyson tree would be a transparent but impermeable outer membrane. Inside the tree waste products would need to be recycled by symbiotic organisms; human beings would probably count as one such symbiote, as they produce carbon dioxide and other wastes which the trees could utilise. In fact, the inside of aDyson Tree would be essentially a CELSS - A Closed Ecological Life Support System;
http://en.wikipedia.org/wiki/CELSS