I want to add a field to a Campaign which calculates number of CampaignMembers meeting some criteria. In my case, every CampaignMemeber has a checkbox field which shows whether CampaignMember is an existing customer or not. I want to calculate number of customers and display number in Campaign.

How I can do it without writting apex code?

I started creating a field:
1. Chose formula type - I couldn't find CampaignMember object and, as the result, any custom fields, it just doesn't exist. I don't know why? Logically it should be.
2. Chose Roll-up field - I can count number of CampaignMembers but in criteria who'd be included I didn't find any custom CampaignMember fields.

As far as I see now, Campaigns are imature and it differs from other standard objects (e.g. Contacts and Accounts has same relationship). Why?! 

I want to add a field to a Campaign which calculates number of CampaignMembers meeting some criteria. In my case, every CampaignMemeber has a checkbox field which shows whether CampaignMember is an existing customer or not. I want to calculate number of customers and display number in Campaign.

How I can do it without writting apex code?

I started creating a field:
1. Chose formula type - I couldn't find CampaignMember object and, as the result, any custom fields, it just doesn't exist. I don't know why? Logically it should be.
2. Chose Roll-up field - I can count number of CampaignMembers but in criteria who'd be included I didn't find any custom CampaignMember fields.

As far as I see now, Campaigns are imature and it differs from other standard objects (e.g. Contacts and Accounts has same relationship). Why?!