I am an advocate of avoiding stairs in post frame buildings. They both take up space and reduce accessibility to upper level(s) of your building. It is less expensive to construct a post frame building on one level, rather than multi-levels. 

I happen to live in a barndominium (actually more technically speaking a shouse – or shop/house combination) and we have stairs. Lots of stairs, due to our living area being located on our second floor. Our second floor also happens to be 20 feet above grade! We also have two elevators. First of these was a pneumatic “tube” elevator because my lovely bride let me know there is no way she was going to tote groceries up those stairs! Our second elevator is a full sized one, necessitated after my wife’s tragic motorcycle accident four years ago, leaving her a paraplegic.

Back to our case at hand – how much area will stairs take?

For residential (R-3) use maximum rise of stairs is 7-3/4” and minimum run is 10”. 

For sake of this example, we will assume lower floor is going to be a concrete slab on grade. Begin with vertical distance from grade (bottom of pressure preservative treated splash plank) to top of flooring of second floor.  Deduct four inches for concrete floor thickness.

Arbitrarily picking 9 feet for top of second floor, we have 9 feet X 12 = 108 inches. Deducting for slab = 104 inches.

104 inches / 7-3/4 inches of maximum rise = 13.42. Rounding up we get 14 total risers, with our second floor itself becoming number 14.

13 treads remain, at a minimum of 10 inches = 130 inches or 10’6” of horizontal floor space. But wait, there is more!!

A minimum of three feet of space (for a three foot width stairs) must be provided at both top and bottom of stairs, so allow for these areas as well.

For Building Code requirements for stairs, please see: https://www.hansenpolebuildings.com/2015/09/stairs-2/