I've always thought topiaries were a bit too formal and fussy for me. I don't know why my mind changed, but now I think simple circular ones are very pretty and much more interesting than a plain pot of ivy.
Making my topiary was actually quite a simple process. I went to the garden store, wandered around for an hour and came home with a 6" ivy -- plus 3 plants, 2 seed packets, and 2 terra cotta pots.
I repotted the ivy and then raided our spare closet for a wire hanger. It only took about 10 minutes of wrestling to get the hanger unwrapped into a basically round shape, which I then stuck into the pot around the ivy.
Using baker's twine, I grabbed runners ("branches" of ivy) and started tying them to the hanger. If I were starting again, I would have been more selective in the plant I brought home and picked out something with longer runners.
Mine, as you can see, doesn't reach all the way around the hanger yet. There's already plenty of new growth on the tied down runners, and the stuff in the middle that was too short to be tied is now getting long enough. So before too long, I think I will have a super-looking, full coverage ivy topiary!