Metal gives and then fails. Glass gives minimally, and depending on tempering, can fail very, very quickly.
If you are not wearing a seatbelt, you run the risk of being ejected from the vehicle, and the higher risk of being 'partially ejected' from the vehicle, which is often worse.
I personally observed only 1 vehicle where the roof caved in on rollover (I believe it was a mid 2000s mustang). If the driver had been a few inches taller, I imagine he would've been hurt pretty badly.
The only other time I saw a roof collapse in wasn't from a roll over, but striking a tree roof first at a high rate of speed.
The only rollover crash I ever observed that the driver couldn't walk away from was a rather fortunate partial ejection. The vehicle only rolled onto its side, pinning the drivers arm between the road and the door as it slid for a few dozen yards.
The durability of the laminated safety glass should not be understated. A fire department's extraction team's approach is likely to be "cut through the glass with a circular saw".
Granted, all of this is anecdotal, with a very small sample size. Either way, wear your seat belt.