While we (The Pittsburgh Independent Hi-Railers) do not have a large number of members (currently 12, with 1 junior member, and a few prospective future members), we have put up some large layouts. Our current large setup is the annual Holiday Lights event at Kennywood Park in Pittsburgh (usually around 20-21 nights of operation). They give us a roughly 5000 sq. ft. space in which to set up. Here is a shot from our 2019 season:
It is sort of a lop-sided "U" shape, and consists of over 300 feet of track to make a full trip around. Times 4 mainlines, that is over 1200 feet of track.
We have done larger layouts in the past, including a holiday display that occupied a storefront that used to house an Old Navy store in a local declining mall. We also filled Black Hall at York in 2010 at a time when the club only had 8 active members. We have done conventions in a number of different states, and as far away as Las Vegas. We are now in our 23rd year as a club, and hoping that train shows and displays can start returning to normal soon.
Andy