pole shed questions

Consider the grade and any fill that might be necessary.

That's screwing me right now.

I did exactly what you're talking about doing, and I need 6 inches of fill to get above the water level in bad storms.

Bigger problem is that will cause my ceiling to be too low.

I did a 26x30.

If you're considering a structure as large as 40x something, why not plan it in sections, and have 20X graded and slabbed, then add the other half later. After the grading and first section, you could even do the pole barn thing for the second half.