Recommendations to limit access to a page on main domain

I am running a multi site (sub-domains) with BuddyPress.

I would like to use Gravity Forms to create a front end input form on the root domain for members to enter information about their business. The information from the input form will be saved to a custom post type.

I would like to limit access to the front end input form to “Pro” members. I am using Pro Sites.

Any recommendations on the best way to accomplish this?

PS – I prefer not to use the Directory Plugin.