Size chosen to fully utilize the available Bambu P1P plate size. (For utilizing the full 256x256 plate size, see instructions)

Height was chosen to coincide the official LEGO box height (150mm)

You can also check out my other big LEGO box. It's prettier, but more wasteful.

Optimized it to use minimal amount of filament:

Cover:

Infill: Lightning, density: 25%

Brim: No brim

Support: normal(auto)

Filament used: ~200 gram

P1P print time: 6.5 hours

Box:

Infill: Grid, density: 25%

Brim: Outer only, 5mm

Support: None

Filament used: ~460 gram

P1P print time: 11 hours

Note #1: Prints fine in regular P1P speed, no need for reduced speed

Note #2: I recommend using a glue stick on the entire print surface, because the model is very wide (takes up the entire print surface) and you don't want it to bend while printing.