We have a field on the Account level called "Monthly Fee".  I'd like to create a new field on the parent level so we can see a roll-up summary of the children accounts.  Please help me with writing the trigger! 

We have a field on the Account level called "Monthly Fee".  I'd like to create a new field on the parent level so we can see a roll-up summary of the children accounts.  Please help me with writing the trigger!