Turtle floating island program

I want a program that will build a floating island (just a upside down peramid ) can someone help me I have 0 knowledge on programming in computer craft

I would start with building a simple square.

A square can be built using two for loops and a few turtle commands, for example:

local function buildSquare( nSide )
  --# repeat nSide times
  for x = 1, nSide do
    --# build a straight line nSide blocks long
    for y = 1, nSide do
      turtle.placeDown()
      turtle.forward()
    end
    --# turn around
    turtle.turnRight()
    turtle.forward()
    turtle.turnRight()
    turtle.forward()
  end
end

buildSquare( 5 ) --# build a 5 x 5 square