2 rows of 5 evenly spaced. Chain hang so they are level. Keep the short end about a foot from the ceiling.
So on the short side of your building, you would start 6.5' from wall and install one then 12' space then install one. 6.5' * 12' * 6.5'
Long side would be 3 foot from the end then 6' on centers. 3'* 6' * 6' * 6'* 6'* 3'
* represents the light.
Graphic representation below.
__ __
__ __
__ __
__ __
__ __
You may need to add a couple for task lighting in certain areas, but that layout will give you uniform lighting through out.