Hello Chris Carrier,
Although there is no permissions that needs to be set to explicitly allow/deny users to add custom fields for content modules, the setting is visible only to Administrators. Thank you for pointing out the need for custom roles, we have discussed it internally and logged a task for implementing such functionality for the future releases. Once again thanks a lot for the constructive feedback, and please excuse us if any inconvenience has been caused.
the Telerik team
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