It was a 101 over the weekend in Houston, when we went to lunch we parked the car on tarmac in full sun. About an hour later, we kicked off cabin cooling as we left the restaurant. By the time we were at the car (3 minutes), the car was cooling well (probably around 82 and dropping fast) and it started at 105 (overheat protection is on).
Pretty much never even think about the roof being glass as I never notice much of any heat intrusion once the A/C is going. Yes it will warm up in the sun and heat, but my previous cars did that in Houston and they had metal roofs or fully shaded sunroofs. Previous cars did not have pre-cooling or overheat protection, those two features make the Model S great in Texas.
Much more heat comes in via the windshield - clear ceramic film there helps a lot . Alternatively, you could get a windshield sunshade for when you park outside.