Furniture assembly in Toronto usually happens in a room that was built long before flat-pack existed. I work in the old city every week, in Riverdale semis, Annex apartments and Parkdale walk-ups, where the floor slopes and the doorway is narrower than the box.
I bring the tools, sort the hardware, build the piece where it will stand, level it against the floor you actually have, and anchor it to something solid. Then the cardboard leaves with me. Free quote first, and the price is agreed before I start.