Look in the library, there will be other dissertations for you to look at. I am sure that you will have been given examples already by tutors. If someone gives you a topic then it is not your own idea! Surely now that you are in your final year you must have thought up one topic that you can explore. Maybe you should have a look round at the buildings in the city where you are studying and see what ideas jump into your head! Think about magnificent structures elsewhere in the world and explore how they came about and the design / structures / work that must have had to be undertaken to achieve the end result. At the end of the day you have to work for a degree and a dissertation should be full of your own work and ideas and existing theories.
