You might prefer to have polarities on opposite sides of a cube, or you could have each cube be a single polarity, or just throw them in randomly like I did !

Might need a brim if you don't trust your bed adhesion, and some minor cleanup on overhangs to slot in the magnets. If they don't set in firmly, a drop of superglue should be more than good enough to keep them there.

Cubes are 20mm per side, fitting 8x2.8mm magnets on each face. About 5g per cube.

These are the magnets I used (not affiliate)

If you want another magnet size, within reason, I'd be happy to add that too.