If you are looking for a ready to use platform, I would recommend using a web hosting billing system like Hostbill or WHMCS.
According to their official website, HostBill lets you automate provisioning of DigitalOcean’s droplets, providing your customers with nice client area GUI to control their services. The client panel offers the variety of possibilities, from creating and destroying the droplets to setting SSH keys and injecting them to droplets. Admin area on the other hand lets you keep everything under control, from billing details, through the account lifecycle to client area sections access.
For more information, you can visit the this page here:
If you prefer WHMCS you could use a module like this one:
Also, DigitalOcean provides an API that you could use to automate provisioning new servers, you could use and create your own webhosting billing system.
Hope that this helps!