I'll take a stronger position than Jay on Hammer Beams, don't do it. They are implemented poorly more often than correctly. They work out for a few years, long enough to get on the cover of your favorite timber porn magazine but invariably they begin to buckle and spread. The ancient cathedral builders knew this, or at least the ones that built those that still stand. They build massive stone buttresses on the outside of the cathedral to counter the horizontal thrust. Even when you account for this they tend to twist (buckle) out of plane unless stiffened perpendicularly. It can be done right with a specialty timber frame engineer and lots of hardware at the post foot, reinforced foundation, and massive support posts.