You can specify the height of the unit to be what ever you want, but 72 inches is the most commonly specified height. The general rule is to go at least as high as the shower head. The hardware should not be seen over the top of the unit. Normally the door is mounted on a 4-6" curb, so if you are measuring for an ADA barrier free shower which doesn't have a curb you should be making the enclosure 76-78" to achieve the same coverage. If your tile doesn't go to the ceiling don't take the height right up to the top of the tile, or try to line up a the top with decorator tile. You may have a perfect match on one side, but be off by a ittle bit on the other side. Your eye can see this difference, but if you back off a 1/2" the deference isn't as noticeable. If there are mirrors in the bathroom check how the unit will look in the mirror.