Mob Trap Builder

-- 0.4

local fuelLevels = turtle.getFuelLevel()
local selectedBox = 1

function shaft()
    for i = 0, 19, 1 do
        for i = 0, 3 do
            placeBlock()
            turtle.turnRight()
        end

        turtle.up()
    end
end

function placeBlock()
    if not turtle.place() then
        selectedBox = selectedBox + 1
        turtle.select(selectedBox)
    end
end

function placeBlockDown()
    if not turtle.placeDown() and turtle.getItemCount(selectedBox) == 0 then
        selectedBox = selectedBox + 1
        turtle.select(selectedBox)
    end
end

function nextPos()
    turtle.turnLeft()
    turtle.forward()
    turtle.turnRight()
    turtle.back()
end

-- buildshaft
shaft()

-- get in position to build platform
turtle.up()
turtle.forward()
turtle.turnRight()
turtle.back()

--start building platform
for i = 0, 8, 1 do
    for j = 0, 3, 1 do
        x = 3 + (2 * i)

        for k = 1, x, 1 do
            placeBlockDown()
            turtle.forward()
        end

        turtle.turnRight()
    end
    nextPos()
end