square_count = 20;

module DropCubes(square_count) {
  num = floor(rands(0,4,1)[0]);
  
  if (num < square_count) { 
    for (y=[0:10:num*10-1]) {
      translate([0, y, 0]) cube(5);
    }
    translate([10, 0, 0]) DropCubes(square_count - num);
  }
  else {
    echo("Ended with", square_count, "squares left.");
  }
}

DropCubes(square_count);