Grout spacing for large format wall tiles
I think that 33.3 cm x 100 cm (13.1 inch x 39.4 inch) large format tiles will actually look good with a 3 mm (1/8 inch) grout line.

The builder is probably using clips to hold the tiles to the wall, and the ones I've used are thicker than 1 mm. These clips help make the tiles flush with each other as the tile adhesive/thinset dries. If they install them without using clips (or another system) it will be exponentially more difficult to install well. 

If you want the grout spacing smaller than 3mm, I would ask the builder what the smallest spacing they can do without extra work with their clip system, and ask them if it's possible to use another clip system that would work better?