Hi Ben,
Thank you for opening this thread, if I understand correctly you have given the Organization Administrator role to one of your users but he can’t see any IAM roles nor have informations about quotas.
It might be confusing but “Organization Administrator” translates to “roles/resourcemanager.organizationAdmin”[1] which have permissions over the ressources but not over the IAM roles. To obtain the “iam.roles.list” permission one would need an IAM Roles role [2] like “roles/iam.organizationRoleViewer”.
Likewise, to have access to all the quotas information on would need to have a Service Usages Roles[3] or a quota permission on a specific product.
I hope that will help!