The closest in my experience was probably working with customizable digital WooComerce products. Users edited the product on site and then purchased the customized version.
From technical point of view my implementation did the following:
- Stored ongoing (before purchase) customizations in user meta
- On order paid detached customizations from user and transferred them to order meta
That way users retained access for exact state they paid for and file could be generated again for them on demand from order page.
Where it started to bog down was allowing users to customize and purchase multiple versions of same product in one order. At that point requirements just shoot out of what was reasonable scope under circumstances.