How does the roof have 0 elevation gain? Or do you mean where the water is to where it's going is 0 elevatiom gain? If so this pump is way over kill.
I'm struggling to understand your setup based on this message, a simple drawing would help.
Discussion
There's a picture attached. 2 IBCs stacked at the barn, I need to irrigate a 100ft W by 500ft L area.
You’ve got me thinking:
The barn is ~25ft tall. It will have eves. Why does my storage need to be at the barn? I need pressure more than anything. Why not put 4 ibcs 250ft out then irrigate from there?
The height from the barn will suffice to push the water to the ibcs then I can build my system from there.
1 manifold feeds the entire system. 
Is the horizontal what you need to irrigate? Is there any elevation drop there? If you just put your IBCs at the highest point, you will not need a pump with 275x4 gallons of pressure.
I would recommend putting the IBCs at the barn to top feed them straight from the gutter, otherwise you will need a pump to go from the ground to the ibc tote top. Bonus points if you put them on the north side to block the sun. More points if you both paint them black and wrap them to eliminate algae growth. Both are needed, I see systems with one or the other and the sun still leaks in.