Often a man will surprise a woman with an engagement ring to make it "official." Sometimes it's a family heirloom, which then will need to be sized to fit, but the sentiment is more important than the ring fitting at that moment. Sometime I have known the couple will look at jewelry together, but the actual purchase and presentation is a surprise. Sometimes the man will propose then take the bride out to choose a ring ... Maybe that's why simple diamond solitaires are a popular engagement choice - hard to go wrong with something that classic!

Let's see, among my siblings, there was
1 ring chosen by the groom-to-be and presented when he proposed
1 ring the couple chose together
2 family heirloom rings presented then resized to fit.

But I do not know if we are "typical" in any case!