You can get a notification when a material picker changes a material to know which material was selected. If you plan to make material changes with your custom API based material picker, you will also know which material the user selected.
Shapespark has limited capabilities for changing objects. Basically all the objects need to be present in the model and you can use Views functionality to hide/show different options. If you do so, there is an API call which will allow you to get a notification when the view is changed.
So on the Shapespark side this is doable if the limited object change capabilities are sufficient for you. Assembling the information into a PDF/text would be more programming work and require some backend support, but this is independent from Shapespark functionality. You will need to use or program some service that would transform the information about the selection into a document and send it to you. A simple approach could be to assemble such document in a browser and ask the client to mail it to you, this way you wouldn’t need a backend support.