So, size was reduced to keep a manhole accessible, then to comply with building fire regs, each losing 1x brick from the 5m length, so 2 bricks shorter. Was agreed in principle as foundations had already been dug at the larger (5m) size, then inspections required it to shrink. @nod, Agreed that I've not got what ordered, that's the reason for my questioning. Work is good, although wasn't without hickups during build.
@Mr Punter, 4.6 x 3m rectangle, from 5x3, so 8% shorter externally. This also changed roof aesthetic which includes 2x skylights, which are closer than designed.
Again, please, just looking advice, not abuse.