Hi Peter,
Maybe the first thing to do is to speak to the architecture department to see what kind of things they are looking for in a portfolio. As you intend to study architecture, I would focus a portfolio on what 'architecture' means to you: how are materials used in an innovative way; what is the interplay between a building's interior and its exterior; what forms and lines are used and what interaction is created by the use of space/negative space; how does the form of the building dictate its use (ie is it a public space, museum, office, church); what gives a particular building or structure that 'wow' factor; what are the challenges that confront an architect in terms of materials used and how far the boundaries can be pushed etc etc.
If you want inspiration on how to shoot images with an architectural theme, have a look at the work of Anthony Weller, David Churchill, Adam Lawrenson, Paul Freeman and
www.fotohaus.co.uk for starters.
Hope this helps!
Regards
Denise