When I did our basement I put the walls up first and then did the subfloor. The subfloor that I used (www.subfloor.com) said to leave an “expansion gap” around fixed objects.. so I figured if the walls held the sublfoor down it wouldn’t be able to expand and might pop up in the middle of the room. But I could have done it wrong..I’m no pro.. that was the only time I ever did anything like this!