Simple AutoLisp script to draw some common LEGO parts.

brick.lsp

(defun c:LEGO ( / name)
    (if (setq name (getstring "Enter component Name (Brick/Plate/round_brick/round_plate)"))
        (if (or (eq name "plate") (eq name "P"))(draw_plate)
        (if (or (eq name "brick") (eq name "B"))(draw_brick)
        (if (or (eq name "round_plate") (eq name "RP"))(draw_round_plate)
        (if (or (eq name "round_cone") (eq name "RC"))(draw_round_cone)
        (if (or (eq name "round_brick") (eq name "RB"))(draw_round_brick))))))
    );end if
)

(defun draw_brick ( / P)
    (graphscr)
    (setq P (getpoint "choose the starting point"))
    (command "osmode" 16383)
    (setq M (getint "Enter Row Number"))
    (setq N (getint "Enter Col Number"))
    (command "osnap" "off")
    (__brick_like P M N 9.6)
    (command "osmode" 16383)
)

(defun draw_plate ( / P)
    (graphscr)
    (command "osmode" 16383)
    (setq P (getpoint "choose the starting point"))
    (setq M (getint "Enter Row Number"))
    (setq N (getint "Enter Col Number"))
    (command "osnap" "off")
    (__brick_like P M N 3.2)
    (command "osmode" 16383)
)

(defun draw_round_brick ( / P)
    (graphscr)
    (command "osmode" 16383)
    (setq P (getpoint "choose the starting point"))
    (command "osnap" "off")
    (__round_brick P 7.9 3.9 T)
    (command "osmode" 16383)
)

(defun draw_round_plate ( / P)
    (graphscr)
    (setq P (getpoint "choose the starting point"))
    (command "osmode" 16383)
    (command "osnap" "off")
    (__round_brick P 1.2 3.9 NIL)
    (command "osmode" 16383)
)

(defun draw_round_cone ( / P)
    (graphscr)
    (command "osmode" 16383)
    (setq P (getpoint "choose the starting point"))
    (command "osnap" "off")
    (__round_brick P 8.0 2.5 T)
    (command "osmode" 16383)
)


(defun __brick_like (P M N height / start x y P0 P1 Pc base tmp iter_x iter_y)
    (setq x (- (nth 0 P) 4.0))
    (setq y (+ (nth 1 P) 4.0))
    (setq z (- (nth 2 P) 1.6))
    (setq P0 (list x y z))
    (setq P1 (list (+ x (* 8.0 N)) (- y (* 8.0 M)) z))
    (setq Pc (list (+ x 4.0) (- y 4.0) (+ z height)))
    (command "box" P0 P1 height "")
    (setq base (entlast))
    (setq iter_x (nth 0 Pc))
    (setq iter_y (nth 1 Pc))
    (setq iter_z (nth 2 Pc))
    (repeat M
        (repeat N
            (command "cylinder" (list iter_x iter_y iter_z) 2.5 1.6 "")
            (setq tmp (entlast))
            (command "union" base tmp "")
            (setq base (entlast))
            (setq iter_x (+ iter_x 8.0))
        );end repeat N
        (setq iter_x (nth 0 Pc))
        (setq iter_y (- iter_y 8.0))
    );end repeat M
)

(defun __round_brick (P height top hollow / base tmp)
    (setq x (nth 0 P))
    (setq y (nth 1 P))
    (setq z (- (nth 2 P) 1.6))

    (command "cylinder" (list x y z) 3.2 1.6 "")
    (setq base (entlast))

    ;(command "cylinder" (list x y (+ z 1.7)) 3.9 height "")
    (command "cone" (list x y (+ z 1.6)) 4.0 "T" top height "")
    (setq tmp (entlast))
    (command "union" base tmp "")

    (command "cylinder" (list x y (+ z (+ height 1.7))) 2.5 1.7 "")
    (setq tmp (entlast))
    (command "union" base tmp "")

    (if hollow
        (progn
          (command "cylinder" (list x y z) 1.55 11.3 "")
          (setq tmp (entlast))
          (command "subtract" base "" tmp "")
        );end progn
    );end if hollow
)