More Detail
Pole buildings by their inherant design are a monocoque construction. That is, they are a type of construction where the outer shell carries the major stress. The poles, trusses, purlins and girts all play a supporting role, but it's the steel that ties all other components together that brings it to a final rigid conclusion.
Standard ribbed pole barn steel in most cases comes 3' in width by whatever length you request. It is relatively easy to cut across the width of the steel (crosscut) with standard issue snips, but extremely difficult to cut the length (rip) without special and expensive power tools, ie power nibblers and shears.
That being said, it is easier to design your building around the width of the steel rather than making the steel fit your building!
All dimensional lumber has its length determined so that it lays out to accept standard 8' plywood with minimal waste. That's why most lumber stores carry 2x material in 8, 12,16 and 24 foot lengths. Now enters the pole barn with 3' steel that rejects 1/2 of the dimensional lumbers lengths. Therein lies the conundrum, how to address both of these issues with a minimal of waste. The best answer is to design a building width and length that is divisible by both 3 and 8. The ideal building would be 24' x 24' or 24' x 48'. But that doesn't always lend itself to fit the footprint, the area available or the budget you have for the building. The next best solution is to design a building where the width and length are divisible by 3. Because steel costs considerably more than dimensional lumber, it is not only economically feasible to have the ends of a few 2x's laying around at the end of a job than strips of steel, but also prudent because you can utilize, in other projects, the 2x cut offs more readily than you can the strips of steel.
That's my detailed answer on why you should consider a building that minimizes the cutting of steel. I base that answer on my experience of designing and building many pole buildings professionally. If you would like further detail in the layout and construction, I would be glad to offer it.
