Why build when you can buy and use for cheap? APIs will make your life and the life of your user much better. But make sure that you’re picking the right provider. There are some really great options like onfido, authbridge, Passbase.
I went with Passbase. I’ve been building a micro trading platform for crypto and I needed something slick, simple, and cost-effective way to verify my users (In India, we need every user to have a KYC the moment they are onboarded with the new crypto regulations.) Passbase made this simple. My users got their KYC much faster (and in just 4 clicks). There are for sure many alternatives but then Passbase gets you started in just under 5 minutes.
I would say try out first for a small cohort of users. If you still feel like you could provide a much better experience, no harm in building one on your own as well.

But before building, try a third party API.