that is a cute lil tank, and if done on a much larger scale would be just fine for the goldies.
i toyed with the idea of making lego caves for my 10 gallon betta tanks back in the day, but my kidlett confiscated the bucket of garage sale lego on me! lol. i bought that lego for the finkids dagnabit! oh well, didn't have enough lego to make a cave for my oscar anyway.......