When I was showing, I had two calves per year, and I had a cool room measuring 12*14*9. This is a great size for two calves but would be less than ideal for three. Notice that the height of this cooler is 9 feet. I highly recommend, at least, that height. I have been in coolers that are only 6 feet tall, and they are extremely unpleasant. Additionally, a 9 foot ceiling allows for a grooming chute if the room ever doubles as a clipping room.
The calves were free to roam. The advantage of this arrangement is that your calves get some exercise, even in the cooler, and they are also bit happier. The disadvantage is that your fans are not directing the calves' hair straight forward. However, both arrangements work.
I ran a 2.5 ton cooler unit and three turbo fans. The cool room had a dirt floor with around six inches of mulch. Additionally, do not forget to have an exhaust fan. And if at all possible, have some sort of emergency alarm system for if you lose electricity or if your cooler unit fails.
This arrangement worked well for me.