im building a patio cover attached to my house i have alredy poured the cement and placed the post brackets (6x6) 12' apart the distance from the house to the post bracket is 16' in lenth leaving a 2' overhang that will make the rathters 18' is that to long of a span? also what size header should i use
It's a start, BUT I don't know why you started anything without a complete plan in place. Which, begs the question, is any of this "permitted" or approved by your Municipality? GRAVE mistake, if it's required and hasn't been obtained. Attachment to the house or piers may be inadequate.
You'll need a minimum of 2x8's for the headers (8x1.5) and they should be doubled and 2x12's (12x1.5) for the rafters, which will also likely need to be doubled due to splicing of shorter lumber to achieve the distance. If that's the case for the rafters, you may be able to take the rafters down to as little as 2x8's.