Buying a two-family: what the roof is telling you
On a two- or three-family the roof is one of the largest single numbers in the deal, and it comes with a condition nobody mentions at the viewing: you will own it, and someone else will heat the top of it.
Five minutes from the pavement
Count the penetrations. Two kitchens and two bathrooms mean two stacks or more, two heating systems mean two flues, and each is a hole cut on purpose. More holes is not a fault; it is a number worth knowing before you own it.
Look at the overhang along the front. Staining on the fascia, a gutter pulling away, or paint bubbling under the eave are the visible end of an ice problem that starts inside.
Look for dormers that do not match the rest of the roof. A dormer added later brings two valleys and two cheek walls with it, and they were fitted to what was already there.
What only the attic will tell you
Whether the boards are spaced or solid, which decides whether the next covering needs a new deck under it.
Whether daylight shows at the ridge, and whether insulation has been packed into the corner at the eave, which blocks the intake and guarantees the ice comes back.
And whether the bath fans discharge outside or simply into the roof space, which is common on converted houses and puts moisture exactly where it does most harm.
Which findings should move the price
A covering near the end of its life is a number, and a fair one to negotiate. Spaced boards under it are a second number on top.
Ventilation and air sealing are usually the smaller figure and the better investment, and they are worth raising precisely because they are cheap relative to what they prevent.
Structure that has moved is a different conversation and needs someone qualified to say so before anyone talks about coverings.
Next step: Roof inspection
None of this replaces an inspection by someone who gets into the attic and onto the roof. It is a list of what to make sure they look at.