This is a contributing reason why I ruled out buying a Model 3.
In Jan 2019, before the SR and SR+ existed, the glass roof was part of the $5K premium package. I wasn't too keen on paying $5K for stuff I didn't want to pay for such as the glass roof as I was concerned about the reports of cracks (there have been numerous reports here on new 3's and some reports of it at work, as well) and leather/fake leather. Sure, Tesla is covering them under warranty but what happens after warranty?
And yes, this is another large piece of glass vulnerable to cracking/chips/breakage from rocks and other debris (e.g. from trees).
Now, unfortunately, all 3's ship with this and there's no metal roof version (yet).
I ended up buying a heavily discounted '19 Bolt (over $6K off MSRP) at end of Jan 2019. Was way cheaper with the $7500 Federal tax credit than a MR 3 ($44K back then, IIRC) + $2K for a color I found acceptable minus $3750 Federal tax credit. (Yes, I'm well aware of 3 vs. Bolt advantages and disadvantages. There were other numerous shortcomings/features I wanted/design decisions I don't like on the 3 that haven't been addressed.)