It is the third gable and the necessary statics for it.
There is no third gable here. If you mean the ridge board by that: it rises in my proposal from a load-bearing wall.
How can a staggered shed roof be priced? More expensive than a hip roof, the same, or less expensive?
Slightly more expensive than a classic gable roof, a hip roof is significantly more expensive. Compared to the classic gable roof, the "staggered shed roof" is only more complex because of the second ridge purlin (as long as it is built as a rafter roof, otherwise the trusses are basically just divided).