I would use a concrete saw to cut out two foot by two foot squares at each column location remove the concrete auger holes as appropriately designed by the building engineer set the columns in the hole per the plans then form and fill with premix around the top of the column to complete the slab.
Pouring concrete floor in pole barn.
The cost of labor to pour concrete is 45 per hour.
This can prevent damage caused by a pre mix concrete truck.
Since there are no foundation walls in a pole building a floating slab can be poured inside the poles using the skirt board for forms.
If the walls are open or you have sliding or overhead doors you can use a 2 4 as a form.
There can also be a delivery fee of 60.
Time lapse video of my 40x60 pole barn floor being poured.
Labor cost for concrete slab.
It is best to have the shell of your pole barn completed before you pour a concrete slab.
If a thicker floor is desired excavate below skirt board bottom by any slab thickness greater than 4.
Prior to pouring a nominal 4 3 1 2 actual completed thick concrete slab in building finished graded compacted fill top will be even with skirt board bottom.
Time lapse video of my 40x60 pole barn floor being poured.
I recommend a standard 4 floor for most residential pole buildings.
If you are just storing toys lawnmowers and cars in the pole barn then 4 of concrete will more than suffice.
Concrete slabs are poured either off or on the job site.
If your pole barn has solid walls they will serve as forms for pouring the slab.