Hi Matt, for my Part 1 Dissertation topic I covered Japanese Architecture and sustainability and came across Shigeru Ban, one of Japan's most prominent architect involved in sourcing a range of green architectural solutions into his projects.

Check out the Nomadic Museum in California: http://www.arcspace.com/exhibitions/colbert/nomadic.html

If you are going down the sustainability route then the key to finding the right topic for discussion in your dissertation is focus. The Sustainability topic spans such a wide spectrum ranging from a greener way of living to the latest sustainable architectural solutions, so therefore you need to find the core substance which will drive your dissertation forward. Perhaps start by brainstorming 'WHAT' area of sustainability you are interested in and relating this to another area of architecture which also interests you.

Hope that has helped :)