The Ego is an interesting area to explore and certainly we can see examples of the architect and his ego displayed in films and the monuments they design. You might want to discuss the psychological aspects of ego and relate to pieces of architecture that represent ideas of ego and monument. Architects have been criticized for building monuments to themselves. you might want to argue for architecture that deals with the needs of the people and a more socially constructed architecture.
There is a little book called Ruins by the Whitechapel Gallery/ Documents of Contemporary Art that discuss the idea of the monument particularly in relation to modernist utopias and ideals where steel and glass structures were established. there is also the idea of monumentalize that is discussed in relation to architectural movements. You might be able to locate this via the library: The Architects’ Journal, Volume 205, Issues 9-16. However, there are quite a few research choices if you use keywords of architect ego, monument, monumentalize. Anthony Vidler and Peter Eisenman would be useful theorists to explore on these issues. Also don’t forget the film fountain head used in the lecture on film and function, which you could use as an example.
Use the language and visual inspiration from your research to develop your manifesto further. The text and visual elements need to work together in an integrated way. You don’t need to write as much as 500 words for the manifesto now that you have made a start. the main thing is to resolve it with the creative language, style and visuals you use.