Wood clamp cover is sagging

...I have a question ;). The previous owner of the house (Hartl prefab house) that I bought removed the wall between the kitchen and the dining room.

Now the wooden beam ceiling is sagging slightly right there - about 3cm over 4m length. Above that is only the unfinished attic area.

A builder told me that I could fix this like this:

Lay glued laminated timber (glulam) beams on the ceiling from the attic (over the entire length) and screw them to the ceiling.

Do you have any other solutions? How thick and what kind of wood should the glulam beam be?

I was thinking of a thickness of 15x15 cm over the length (about 5 m). I would screw this completely from below (screws through the ceiling and the glulam post) and tighten it with a locknut.

Thanks in advance for the answers and suggestions

Best regards, Gerald :)

I think it would be more important to find out whether the removed wall was load-bearing. The roof has to rest somewhere as well. We do have load-bearing roof beams that rest on interior walls. If that is the case, it is not sufficient to just lay some wood on top (!). It would need to be properly supported. Normally, the necessary information can be found in the house's structural analysis. Alternatively, a structural engineer would need to take a look. Anything else would be too much of a gamble for me.