Davis Tent & Awning's standard rental tent is a 14' by 16' and they rent a bunch of them.

Unless you are going for a spike camp set up where weight and volume of all your ancillary stuff will be automatically pruned by the long trip in, by all means go for something that is big enough (or even a little to big if you are not sure. 14 x 17 is a good number when it comes to working cots around the perimeter. 14x16 in a squeeze. The graph paper idea is a very valid one. Generally cots around the outer walls and "stuff" in the center is the winning formula.