"LEGOs" is wrong, LEGO is an uncountable noun (like sand, water, rice ect.).
You wouldt say that you are boiling "a lot of rices", or "one rice".
You'd say "a lot of rice", or "one rice grain"
In the same way you also can't claim to have a box with "a lot of LEGOs", or "one lego".
What you have is "a lot of LEGO", or "one LEGO brick"