I don't know if this is the oldest building in Birmingham, or even the oldest building I know, but I visited this lovely Church today and it seemed appropriate to post it for this topic.
It is St. Paul's Church in the Jewellery Quarter in Birmingham, an area renowned for jewellery making, which also has some museums housed in former factories. It's a unique area.
The Church was built in 1772 (http://www.saintpaulbrum.org/churchhistory.php) and was where Matthew Boulton and James Watt worshipped all those years ago. They helped to start the Industrial revolution with all the impact on our world since then. Very clever men.
In the 19th century 2000 children attended Sunday School here! Imagine that!
(I think I've got all these facts right, but if anyone knows differently I do apologise!)