local farmData = {
    length=6,
    width=8
}

turtle.forward()
for i=0,farmData.length/2-1,1 do
    for j=0,farmData.width-1,1 do
        turtle.forward()
    end
    turtle.turnRight()
    turtle.forward()
    turtle.turnRight()
    for j=0,farmData.width-1,1 do
        turtle.forward()
    end
    turtle.turnLeft()
    turtle.forward()
    turtle.turnLeft()
end
turtle.turnLeft()
for i=farmData.width-1,0,-1 do
    turtle.forward()
end
turtle.turnRight()
turtle.back()