G.A.O.T.U: The Freemason interpretation

The Great Architect may also be a metaphor alluding to the godhead potentiality of every individual. "(God)... That invisible power which all know does exist, but understood by many different names, such as God, Spirit, Supreme Being, Intelligence, Mind, Energy, Nature and so forth." [7] In the Hermetic Tradition, each and every person has the potential to become God, this idea or concept of God is perceived as internal rather than external. The Great Architect is also an allusion to the observer created universe. We create our own reality; hence we are the architect. Another way would to be to say that the mind is the builder.

Masonic historians such as William Bissey,[4] Gary Leazer (quoting Coil's Masonic Encyclopaedia),[5] and S. Brent Morris,[6] assert that "the Masonic abbreviation G.A.O.T.U., meaning the Great Architect of the Universe, continues a long tradition of using an allegorical name for the Deity". They trace how the name and the abbreviation entered Masonic tradition from the Book of Constitutions written in 1723 by the Reverend James Anderson. They also note that Anderson, a Calvinist minister, probably took the term from Calvin's usage.
Christopher Haffner's own explanation of how the Masonic concept of a Great Architect of the Universe, as a placeholder for the Supreme Being of one's choice, is given in Workman Unashamed:

“ Now imagine me standing in lodge with my head bowed in prayer between Brother Mohammed Bokhary and Brother Arjun Melwani. To neither of them is the Great Architect of the Universe perceived as the Holy Trinity. To Brother Bokhary He has been revealed as Allah; to Brother Melwani He is probably perceived as Vishnu. Since I believe that there is only one God, I am confronted with three possibilities:
They are praying to the devil whilst I am praying to God;
They are praying to nothing, as their Gods do not exist;
They are praying to the same God as I, yet their understanding of His nature is partly incomplete (as indeed is mine — 1 Cor 13:12)
It is without hesitation that I accept the third possibility..
”
—Christopher Haffner, Workman Unashamed: The Testimony of a Christian Freemason, Lewis Masonic, 1989, p.3

Sources Sited:
Wiki and The Genius of Freemasonry and the 20th Century Crusade.