How can I add the amound of road maintanence fee on a deed?

You shouldn't add the amount on the deed because that will lock you in to that amount without allowing it to be changed. Instead you should put in that the owner is responsible for "a road maintenance fee". Give us more info about the situation and we can tell you how to do it.

how can I add the amound of road maintanence fee on a deed?

Something like that doesn't belong on a deed.

The amount that road maintenance costs today might not buy you a spoonful of dirt sixty years from now.

Who is agreeing to do road maintenance? Do the parties want to bind themselves and their heirs to this deal forever?