If you are lucky enough to have average sized feet then you have a lot more choice, the normal High Street store will cater for people up to about a size 8-9 although I believe that Saxone caters for up to size 10.
On the other hand if you want something a little larger or sexier then your choices are limited, although there are quite a few places on the web offering larger sizes in fashionable styles.
You can normally order the same as a real girl sizewise so there should be no problems.
The one thing to remember is the heel size, if you want to go out walking around town then it is not very wise to have a 4-5 inch heel, you would be much better with a 2-3 inch. By all means have the higher ones for partying etc., but it will kill your feet to walk around town all day in really high heels ;-(