Plan Custom Fields

Plan Custom Fields

Hello Again, 

We have a need to show plans depending on size and revenue of a company. We will not be showing all plans as default.  Is there a facility to maintain such logic within Zoho so we can grab plans that are appropriate to display on our web end?  I was thinking we can solve this using custom fields on plans. is that the correct solution? How do we even add custom fields. I dont see that option on my zoho biling plan pages.