width = 5
length = 23

turtle.select(1)

tLeft = true

function turn()
    if tLeft then
        turtle.turnLeft()
    else
        turtle.turnRight()
    end
end


function step()
    turtle.placeUp()
    turtle.forward()
    if turtle.getItemCount() == 0 then
        turtle.select(turtle.getSelectedSlot()+1)
    end
end


for row = 1, width do
    for i = 1, length do
        step()
    end
    turn()
    step()
    turn()
    tLeft = not tLeft
end