I am completely new to Apex and could really use some help with what seems to be a simple task.  I have a formula on the contact, Persona_True__c, that returns a 1 if the custom field "persona" is populated and a 0 if it is blank.

I would like to have a roll-up summary that sums this field at the account level in a field called Related_Personas__c.  

Because we can't roll-up from contact to account I'm reading that this type of action needs to be a trigger, but I don't even know where to start.  Does anyone have any thoughts or expertise they can share to help me out?