15x15 Square

local pos = 1
local count = 0

function check()
    if turtle.getItemCount() == 0 then
        if pos ~= 15 then
            pos = pos + 1
        else
            pos = 1
        end
        turtle.select(pos)
    end
end

function light()
    turtle.select(16)
    turtle.placeDown()
    turtle.select(pos)
end

function place()
    for i = 1, 15 do
        turtle.forward()
        check()
        if count % 8 == 0 then
            light()
        else
            turtle.placeDown()
        end
        count = count + 1
    end
end

function right()
    turtle.turnRight()
    turtle.forward()
    turtle.turnRight()
    check()
    if count % 8 == 0 then
        light()
    else
        turtle.placeDown()
    end
    count = count + 1
end

function left()
    turtle.turnLeft()
    turtle.forward()
    turtle.turnLeft()
    check()
    if count % 8 == 0 then
        light()
    else
        turtle.placeDown()
    end
    count = count + 1

end

for i = 0, 13, 2 do
    place()
    right()
    place()
    left()
end
place()
left()