Roof

turtle.refuel()
local spot = 1
while true do

while turtle.detectDown() == false and
turtle.detect() == false do
  if turtle.getItemCount() == 0
    then spot = spot + 1
    turtle.select(spot)
  end
  turtle.placeDown()
  turtle.forward()
end

if turtle.detectDown() then
  turtle.back()
 end

turtle.turnLeft()
turtle.forward()
end