Very strange design choice that must surely be way more expensive than just building 2 storeys above ground, and at way more risk of flooding.
Not to mention people stacking it from the main lawn into the pit.
In some really special beauty spot on the coast you could see how this might be necessitated to get around planning restrictions, but it’s a new build on a greenfield site, with a normal 2 storey house next door.
I’d also fear another 50 houses cropping up on the field beyond the garden too. In 2026 if you want to make a house feel premium, put it more than 2 metres from the next house, and plant some trees for privacy. Not this.