It really depends on what kind of tree frog you're looking to get. If you're looking at greys specifically, I keep mine between 68 and 75 Degrees F but they can handle a pretty wide range of temps. Other types of tree frogs will have different needs.
EDIT - I keep my greys around 60% humidity, sometimes down to 50% in the winter. Again though, different tree frogs will have different needs. Greys just come from such a wide range that they can tolerate more. Other tree frogs are less forgiving.