We are going to rebuild our deck and want to be able to upgrade it to an all season room in the future. We are going to used treated lumbar for the structural portions. What size lumbar do we need to use to span 12 ft. Do I need to bulk up the posts currently there are 4x4s. The deck will be 7' off the ground on one side and 10' on the other. Any suggesions wound be appreciated. Thanks