How about this?

            | singular | plural
    nom     | legum    | legi
    voc     | lege     | legos
    gen     | legi     | legorum
    dat/abl | lego     | legos

Depends, there are legos: technik, Duplo, standard, space, etc.

But multiple lego bricks are just lego

Lego bricks/elements

lego = lego : lego