What do you need to provide a good outdoor habitat for you're turtle?
Firstly you will need to figure how where do you want the pond? Outdoor or Indoor? How much do you want to spend? The design? Once you have figure that all out, then you are going to need to research how to build a pond , how to provide a perfect balance ecosystem, and how to clean the pond. Once you have research the four main things, then go find a professional pond landscaper in you're local area. Once you found a right pond landscaper, consult with the pond landscaper what you want!
Once the Pond Landscaper is finish with your dream pond, get you're turtles in the pond! And enjoy the view of the pond, the turtles, and the wild nature that will be attracted to the pond!
You may build it on you're own pond if you don't think you could afford to hire a professional pond landscaper and pay fees. Just MAKE sure you research about building pond you're self! Do not also go cheap with supplies and do not find shortcut on building the pond! If you do, it will become a disaster, and you will eventually also end up spending more money to the pond. I did this and my parent and myself realize it was a BIG mistake and now we are putting more money toward to the pond until their is no problem with the pond!
Please see: Pond Design Gone Bad