I'm going to tell you how we use 'the' with public buildings.
Often, when we talk about public buildings with prepositions of place,
what we're really talking about is the main
reason that people go there.
If you're at school, at college or at university,
you're studying. Now in British English, if that's
what you're doing, don't use 'the' with the name
of the building. Here are some other examples:
If you're in hospital, you're ill. If you're
at church, you're praying. And if you're in court
or worse - in prison, you're in trouble. If we do
use 'the' in these expressions, then it probably
means somebody's doing something else. 'Natasha's
at the hospital - she's visiting her brother.'
'I'll meet you at the school, then we'll go to
the party.' Now it's not every public building
- It only works for some, but if you're talking
about the most common activity, don't use 'the'.
If you're talking about something else, you can.