Modular with sagging ceiling

[Jeremy Albright]

I'm looking at a modular where the 3 tab shingle roof was replaced with a dimensional/heritage type shingle. That has caused (I believe) a significantly greater weight on the roof structure and it is sagging a bit now. Seems sturdy, just sagging in a couple of spots (areas of greater span - open living area as opposed to the smaller bedrooms with less span btwn walls) - Has anyone experienced this? Any issues come about with it? There are no leaks and the roof is in good condition.