Most likely a table... Sometimes floor.

I've got a counter-height kitchen/dinning room table that I use to build on. Works great because I can alternate between sitting and standing. I've been thinking of getting a collabsable sewing/hobby table so I'm not taking up the dinning room table anymore.

My wife and I have an office (hobby room) with each our desks, so I mainly sit at the desk building, though I also use dinner table or sofa when building. It depends on what I am building. MOCs on the desk for sure, bigger models might be built at the dinner table and smaller ones whereever I find fit - like the sofa.