I have the LEGO Taj Mahal sitting here, waiting to be built.
Mine is the old 5922 piece version, a gift from a former BB contributor who fried out on building big LEGOs and sent it to my daughter and I. LEGO has rereleased this set, due to its immense popularity, with 1 extra piece. I believe it is a brick separator.
While not the biggest project in this video, it is still the biggest LEGO set you can buy.
LEGO Creator Series Taj Mahal (10256) via Amazon