Road Constructor

function findFilledSlot()
	for i = 1, 16 do
		if turtle.getItemCount(i) > 0 then
			turtle.select(i)
			return true
		end
	end

	return false
end

turtle.select(1)

while true do
	if turtle.getItemCount() > 0 then
		turtle.forward()
		turtle.dig()
		turtle.digDown()
		turtle.digUp()
		turtle.placeDown()
	else
		if not findFilledSlot() then
			turtle.back()
		end
	end
end