Turtle House Builder

function fuelUp( amount )
    for a = 1, 16, 1 do
         data = turtle.getItemDetail(a)
         if data.name == "Coal" then
             turtle.select(a)
             turtle.refuel( amount )
         end
    end
end
function fuelUpIfNeeded()
    if turtle.getFuelLevel() <= 30 then
        fuelUp(1)
    end
end
fuelUp()
if turtle.getFuelLevel() == 0 then
    error("no fuel")
end
print("How far forward? (z of house)")
zlength = read()
print("How far right? (x of house)")
xlength = read()
print("How many floors?")
floorsno = read()
print("How high is the ceiling of each floor?")
floorsheight = read()
ylength = floorsno * (floorsheight + 1)
print("Working...")
if turtle.detectDown() == true then
    turtle.up()
end
turtle.turnRight()
turtle.turnRight()
for y = 0, ylength, 1 do
    if (y % floorsheight) == 0 then
        for z = 1, zlength, 1 do
        turtle.back()
            for x = 1, xlength, 1 do
                if x ~= xlength then
                    turtle.forward()
                end
                fuelUpIfNeeded()
                turtle.placeDown()
            end
            if z ~= zlength then
                if (z % 2) == 0 then
                    turtle.turnRight()
                    turtle.forward()
                    turtle.turnRight()
                else
                    turtle.turnLeft()
                    turtle.forward()
                    turtle.turnLeft()
                end
            end
        end
        turtle.placeDown()
    else
        for a = 1, 2, 1 do
            for z = 0, zlength, 1 do
                fuelUpIfNeeded()
                turtle.placeDown()
                turtle.forward()
            end
            turtle.turnLeft()
            for x = 0, xlength, 1 do
                fuelUpIfNeeded()
                turtle.placeDown()
                turtle.forward()
            end
            turtle.turnLeft()
        end
    end
    turtle.up()
end