Overlapping Squares Puzzle

The Puzzle:

Overlapping Squares
The picture below was made up from four squares stuck one upon another. I am sure you can see how it was made:

In the diagrams below are some more pictures made from overlapping squares.

Can you work out how they were made? In other words, which square was placed 1st (on the bottom), which was 2nd, etc?
Do you have the answer? Check against our solution!