Most modern Ruby API Client
https://github.com/contactually/zuora-ruby - We spent a good amount of time digging into all of the libraries out there and have been contributing to this one. It is tested and mostly up to date. There is plenty more to support, but it is an actively ongoing project. The ones supplied on Github by Zuora are old, and the autogenerated ones from Swagger are not nice. https://github.com/zuora?utf8=%E2%9C%93&q=&type=&language=ruby
Give it a shot if building your own library isn't ideal and you want to get up and running.