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.
PS: as regards the presentation of the portfolio, it may be an idea to print a hardcover book of your portfolio - they can be done for not too much money. Do an internet search for 'photo books' - photobox has a classic A4 hardcover for only £24. But there are hundreds of companies out there that do this type of thing.
Have you been to the university open day? I went to Newport uni's and was told to use an A3 zip portfolio for photographs, but tihis was for the documentary photography course. Archtecture may be different. Do you have to include sketches as well? Also, if you have just left college or are still in college the tutors should be able to help you compile a sucessful portfolio. I can go back anytime I want to talk to my old photography tutors and they will always help. Hiope you do well and get into the uni of your choice. I am desperate to get on to Newport uni's diocumentary course but its just so expensive to liive away from home.