hi dear. firstly it shouldnt be a cage. make it comfortable for the tortoise as it will be its home. the size of home totally depends on the size of your turtle. if your turtle is 2 to 4 inches big then the size of its home should be 2*3 feet so that it can render comfortably. and yes dont forget to keep water in a dish so that it can drink and soak whenever required. (check the size of your turtle and calculate the size of its home accordingly)