Thickness of slab is 100mm 12.5 x 7.0 x 0.1 = 8.75cu Strip...

Thickness of slab is 100mm
12.5 x 7.0 x 0.1 = 8.75cu

Strip Footing Trenches = 75 liner metres at 0.6m
75(L) x 0.35 (W) x 0.6 (D) = 15.75

Peirs x 5, 350mm round by 2m deep
Pie x 0.175(r2) x 2.0(h) x 5 = 1cu

Total 25.5cu

But because we wanted the house side of the shed slab the height just above the current driveway, the neighbours house side is a bit thicker at the top of the trenches due to the uneven ground. This is where the extra 4cu came into play along with the adding of the 10% buffer to the overall trend widths etc...