The first case is a foundation problem.
Warped roof trusses.
For homes with a unique roof shape trusses are the best choice for supporting a roof.
When i bought my house the garage roof had a sag.
They have issues for a wide variety of reason including damage from wind storms overloading from ice and snow leaks etc.
A bowed truss floor joist or beam looses a great deal of it s strength.
Roof trusses as well as most other framing components must be installed and blocked in order to prevent bowing.
First look for cracked plaster and warped window and door frames.
Trusses offer close fabrication tolerances that benefit homes with complex roof framing configurations.
Trusses are designed to carry the weight of the roof on the ends that is the outer walls.
Sagging rafters can lead to serious problems with the entire roofing system.
This problem occurs occasionally with roof trusses.
It is also very important to find out why the trusses bowed in the first place you may be correct in your analysis that the trusses should have been cross.
In the photos shown the lumber looks like typical framing lumber.
This is rare with an engineered truss system but i do occasionally see some that have broken on occasion.
Therefore giving them a good look is critical when addressing sagging bowed or wavy roofs.
If a seasonal crack opens along a wall somewhere in the middle one or both truss ends are rising or the truss is arching.
One of the most common causes of roof issues are problems related to the rafters or trusses.
Warped truss member from what i have seen in the past the wood used to make trusses is high quality lumber no knots 4 corners clear smooth grain.
2 roof support broken the roof truss or rafter could be warped or literally broken.
Its more common to see a bowed rafter.
If you notice that there is a visible dip in your roof chances are you have a problem with one or several rafters and you may soon be facing more issues like water leaks bowed out walls or your roof caving in on you.