Said to myself that I wasn’t posting on this thread but seriously, throw that guy off site now and don’t be paying him a penny.
His block work is totally novice, I am a building control surveyor and if I walked onto that site I’d be telling him to pull that down and start again, the block bonding is just lazy and the piers are not piers at all, just stacks of blocks inside the main wall.
Why don’t you build it cavity? Why aren’t you putting a damp proof membrane and a screed in the floor? You are spending a fortune on a shed that will be damp and cold, especially if you aren’t plastering the blockwork. Please stop wasting money on this, you could have the job done much much cheaper