Split-level rooflines
The split-level was built here by the thousand, and it has a shape no other house type shares: two or three roof planes at different heights, each one ending against the wall of the section next door. Those walls are the whole story of a split-level roof.
The junction that defines the house
Where a lower roof meets a taller wall, water running down the wall arrives on the roof at the joint, and everything depends on two pieces of metal: step flashing layered into each shingle course going up the wall, and counter flashing set into or behind the wall covering to cap it. Done that way it is permanent. Done with a single bent strip and a bead of sealant — which is what a great many of these houses received at their last re-covering — it has a life of a few winters, because freeze-thaw cycling works on sealant before anything else.
The second split-level trait is short roof runs with low-slope connectors between levels, and sometimes a nearly flat section over an entry or a garage. Shingle does not belong below a certain pitch, and where a builder used it anyway the section has been slowly failing since it was installed.
What to ask for
That the step flashing be replaced rather than reused, and that the counter flashing actually be counter flashing rather than sealant over the top edge. That any low-slope or flat connector be identified and priced with a material appropriate to its pitch. And that the ventilation be looked at as a whole house rather than plane by plane — a split-level has several short attic runs instead of one, and each needs its own intake and exhaust to work at all.