Hi Davit
Sorry for not answering that. A completely custom UI should be fine - we have OData services you can use. There is a odata workbench you can use to create your own services based on any object.
We have some examples of odata usage - this won't show a custom UI, but it will show our odata services.. Look for this published by Prabhat Raman and look at the odata section in this blog: SAP Cloud for Customer Integration with ERP and CRM: How-to Guides and E-Learning
Prabhat Raman - do you have something to add?
-ginger