As a teenager when I did built up roofing they normally lasted 30-40 years.
So roofing is not normaly the culpret.
The problem your having sounds like the vent going through the roof may have a loose joint or even worse a non connected pipe.
Simple test have a roofer/plumber take a garden hose put it down you vent terminal careful NOT to wet the vent piping outside only down this pipe and watch for leaks.
If a leak shows up you know it is a plumbers problem.
Taking a shower and having a leak can be complicated and expensive to locate.
A “shower leak” can be a simple grouting job or tightening a packing nut/gland on the showerbody
Or a drain connection Or the lead pan (I NEVER use plastic crap or fiberglass base) may have a penetration Or the escutcheons were not properly sealed or the installer did a poor piping job using inferior materials like plastic piping. If the garden hose shows the leak the rest is simply opening the walls and ceiling and following the source