The rulebook only says:
Then, turn over the Building and set it aside with the rest of your finished Buildings, if any.
This makes it easy to total up your victory points.
This does suggest they are all visible - which means everyone can see everyone else's. There is also no rule that says how /when you would reveal, just that it ends on the round the 17 point trigger happens :
If you have 17 or more victory points at the end of your turn (counting only Buildings and
Machines, but not Sesterces, Slaves, or Loans), the game will end.
That said, you can always play how you want you just need to agree ahead of time. I think you would need additional rules for how /when to reveal.