Pouring Piers Prior to shed slab.

I am about to arrange my shed slab to go down for a 6 x 9.5m barn.

I will be forming up and prepping the site for the concretes to come in and finish it on the day.

The slab details are 12 piers centers below C sections posts 300mm Dia 750 deep.
SL 72 mesh 40mm cover on a 100mm slab - no edge beam required.

What i want to know is can i have the piers poured separate to the slab and then do my form work following this and pour the 100mm slab directly on top.

I am considering this as due to the time frame between digging the piers and the boxing out ect for finishing and it would be desirable due to the amount of ground water around my place.

I recall the piers for our house were poured separately.

Usualy bored piers are poured first with starter bars for slab but the best person to ask is the design engineer that did the slab detailing.
You mention groundwater, i would be paying particular attention to site drainage

The site was cut out a fw years ago and prepped but is on class M clay. Find a lot of seepage as to be expected on the site. I remember the piers for the house being done separate.

I asked the question after reading the notes as the plan mentions pier depth of 750 if poured separate to slab. Not clear if that is meaning that the piers as a footing for the posts ect and infill slab later or as i mentioned above the slab being done right on top.

I would have expected some form of rebar would be needed in the pier to attach to the slab mesh.

Its a shame the Slab detailing is just a generic one from a shed supply company. Is it something the building surveyor from local council can clarify also do you think?

Relevant Building Surveyor will be able to answer your questions.
You need to understand that M class site can be ruined through poor drainage and become "P"

I had a design done about 2 years ago and have since gone to a different manufacture. I am actually surprised at the difference in the two designs for one slab type with the same shed.

Design 1 included edge beams with trench mesh and SL82 throughout 110mm slab depth and the pires under each post

Design 2 no edge beam, slab is 100mm with SL72 and the piers reduced by 100mm in diameter.

Though it was odd to see the difference and have done some building design study over the years (never finished my diploma and went into electrical design) but with the background in engineering makes me cautious about the revised design and think its with the extra expense of the trench mesh and SL82.

Shed floor should be of similar standard as a concrete driveway, I would go for 110mm +F82 and I would definitely go with edge beam design. You may want to drive and park a loaded truck in there.
You need to remember that if your base is poor or damaged through poor drainage your slab may fail and crack.
The extra cost of materials is minimal but the risk of failure is greater with slimmed down design.
Regulations are about minimum acceptable standard, nothing stops you from doing better.