Not sure how to read your description. At 120'x16', you would have had 8 rooms of equal size with a 16' wall for separation. The "non-beam" (doubled-up 2x4s) you describe must have run across the ceiling at the 8' mark to support the celining joists. The "non-beam" was supported in the wall and the similar "non-beam" butted against it in the wall for the next room.
Without drawing a picture, is that what you meant?
If I heard you properly, removing the interior walls will remove the support for these joist "non-beams" and the roof will collapse. The 120' span requires (1) engineered roof trusses to span the 16' room depth (means removing the entire roof structure and re-building the structure) or (2) posts to hold the proper joist beams (which will have to be bigger than doubled 2x4s due to the 15' span they must support. In essence, you will need posts every 15 feet down the center of the building to carry the roof and celing load.
Can you do #2? Sure. But you better get engineering, drawing and permits. Failing to do so would invalidate your building insurance. Failing to do so might result in a bad rebuild and serious structural issues. You will need to install temporary supports while you replace the doubled 2x4s and anchor the new posts properly. Depending on where you are (California?) you will also have important earthquake protection required or (Midwest, Florida?) possibly tornado or hurricane structure.
Could it be fun? YOU BET! God for it!