If you want a model to work off of, I am personally very impressed with Stripe's API documentation:
https://stripe.com/docs/api
You can see how every single field is described in detail. That's something that the Shopify API documentation lacks. For example, if you look at a Product, very little of it is actually documented. It gives you very prolix JSON examples, but that's pretty much all that's there. For example, if I look at a product's variants, I see the "fullfillment_service" field, which is set to "manual" in all 51 instances that it appears on the page, with absolutely no documentation describing its available values, or even what it does, or how it works.
On the other hand, if you look at the Stripe API, here:
https://stripe.com/docs/api?lang=php#plan_object - You can see that every single parameter is described in detail. It says if it's required, and what it does, the default values, and how to use it.
That's what I'd like to see: Balanced coverage of the API, free of prolixity, with more verbose descriptions, and clean, concise examples.
Thanks!