I did one about five years ago. It wasn't very big, but sure allot of fun to float around in after work, or on the weekends.
It's costant maintenance and after selling the house, it's not something I want to deal with again. Keeping the water clean is a constant, never ending chore. It's not dificult, but with a full schedule, I could go many days at a time and not be there during daylight hours. Miss a few tests and let the water level get out of balance and you have a mess.
Either go real cheap and get something that won't hurt if you change your mind and want to get rid of, or spend allot and get a really good filter system. The actual pools themselves are pretty basic and depending on what style you buy, wont really matter too much. It's all in the filter and circulating the water.
Good luck,
Eddie