Building a 60x36 Barn/Tractor Garage/Shop - Question about Structural Integrity
If you want actual structural advice, hire an engineer licensed to practice in your location. 

For plans that are already engineered for your location, particularly for "agricultural buildings" you might want to consult with your local agricultural extension website, where you might find several hundred choices. 

The plans are commonly free (you already paid for them with your taxes) or very inexpensive. They are very likely to include details you have not thought of, and not to waste extra material where it does little or no good (a common failing of amateur building designers, often combined with failing to apply 10 cents worth of material where it will do five dollars worth of good.)

(note - I play amateur building designer, but I also read Dad's civil engineering books for fun, and have a pretty good idea when I should call in the pros, as well as a better than average knowledge of when &amp; where to apply that 10 cents worth of material due to my reading.)