Rail

local tArgs = {...}
local length = tonumber(tArgs[1]) or 0
local width = tonumber(tArgs[2]) or 0

local slot = 1

function doWork()
    for i = 1, width, 1 do
        for j = 1, length, 1 do
            turtle.dig()
            turtle.digDown()
            place("down")
            turtle.forward()
        end

        turtle.digDown()
        place("down")

        if ( i % 2 == 0 ) then
            turtle.turnRight()
        else
            turtle.turnLeft()
        end

        turtle.dig()
        turtle.forward()
        turtle.digDown()
        place("down")

        turtle.dig()
        turtle.forward()
        turtle.digDown()
        place("down")

        turtle.dig()
        turtle.forward()

        if ( i % 2 == 0 ) then
            turtle.turnRight()
        else
            turtle.turnLeft()
        end

    end
end

function place(dir)
    if turtle.getItemCount(slot) == 1 then
        if slot == 16 then
            print("Put more blocks")
            while turtle.getItemCount(slot) == 1 do
                sleep(1)
            end
            slot = 1
        else
            slot = slot + 1
        end
        turtle.select(slot)
        place(dir)
    end

    if dir == "up" then
        turtle.placeUp()
    elseif dir == "down" then
        turtle.placeDown()
    else
        turtle.place()
    end

end
doWork()