What's the largest LEGO construction ever?
This house is the biggest lego ever built unless proven otherwise.
I searched a bit and could not find anything using more bricks.

Here are some other project falling short from the 3.3 millions bricks :


Shopville Le Gru,Grugliasco (Italy), 1.5km long, using 2,901,760 bricks, 13 February 2005
LEGO Millyard Project at SEE Science Center in Manchester, 3 millions bricks, permanent


Here is a list of LEGO records : http://www.recordholders.org/en/list/lego.html