I think the square format works well here because of the way you have composed the frame. The angle of the floor- and roofboards helps, and of course the pillar on the left is vital for the composition to work.
For many years I used a Hasselblad 501, and after a while i fell in love with the square format. It is a more demanding format than rectangular, photos can easily be static and boring, but when it works the results can be great.
I suddenly got an urge to find my old 6x6 negatives and scan some of them.