What you can see, and what you cannot
A finished roof hides most of the work that decides how it performs. The deck, the underlayment, the nailing pattern and the way the flashing laps are all under the shingles. Nobody can confirm those from the driveway, and that includes us.
What you can see is the outside of the work: the lines, the edges, the metal at walls and chimneys, the collars on the pipes, the vents, and the underside of the deck from the attic. Those are enough to tell you whether the crew was careful in the places that show.
Ask for the photographs. Most crews take pictures during tear-off and install. Pictures of the bare deck, the underlayment going down and the flashing before it was covered are the only way to see the hidden layers after the fact.
Stay off the roof. Everything in this guide can be checked from the ground with binoculars, from a ladder at the gutter line, or from inside the attic.
Lines, edges and drip edge
Stand at the corner of the house and sight along the eave and the ridge. They should run straight. A ridge that wanders or an eave line that dips usually points to the framing or the deck rather than the shingles. It is worth asking whether anyone noticed it during tear-off.
Look at the courses across the face of the roof. The exposed rows should be evenly spaced and run parallel to the eave. A small wobble that only shows in low evening light is cosmetic. Rows that drift noticeably, or a course that is visibly wider than the ones around it, are worth a question.
Drip edge is the metal strip along the eaves and the rake edges. From a ladder at the gutter you should see it on every edge. At the eaves the underlayment should lap over the drip edge, so water running down the underlayment lands on the metal. At the rakes the drip edge goes over the underlayment. If you cannot tell the order from what is visible, the install photographs will show it.
Missing drip edge is not cosmetic. It is the part that keeps water from curling back under the first row and into the fascia and the edge of the deck.
Flashing, boots and vents
Where the roof meets a wall, a chimney or a dormer, look for metal. Step flashing shows as a row of small metal pieces running up the wall, one per course, usually with siding or counter-flashing over the top. A line of caulk or roofing cement along the joint with no metal visible is a different thing. Sealant has a place, but it does not replace flashing, and it hardens and cracks in this climate.
Check every pipe that comes through the roof. Each one should have a boot seated flat on the shingles, with the collar snug around the pipe. Count the pipes from the ground, then count the boots. Old boots reused from the previous roof are worth raising. The boot is the most common place a roof leaks, and a replacement is the time to renew them.
Valleys should look clean and consistent. Whether the valley is open metal or woven or cut shingles, the line should be straight and there should be no exposed nails in the channel where the water runs.
If the roof has a ridge vent, it should run continuously along the ridge, and the slot under it should be cut through the deck. You can confirm the slot from the attic by looking for daylight along the peak. Then check the intake side. The soffit vents under the eaves should be open, not painted over, and not blocked by insulation pushed against them from the attic side.
A bead of caulk where flashing should be is not a repair choice. It is a question worth asking before the paperwork goes in.
Nails, the attic and the cleanup
From the attic, look up at the underside of the deck. You will often see nail points that missed the framing and came through the wood. Some of that is normal. A lot of them in one area, or nails that are bent over or sitting crooked, is worth photographing and asking about.
Outside, look at the underside of the overhang along the eaves. Nails poking through the soffit or the exposed boards at the overhang mean the fasteners were too long for that spot. It is usually more of an appearance problem than a leak, but it is easy to raise now and harder later.
Look across the shingles for nail heads you can see. Exposed nails on the face of the roof, outside the ridge cap, are a leak point and should not be there.
Walk the lawn, the driveway and the beds. A careful crew runs a magnet sweep before leaving and clears the gutters of nails and granules. Loose fasteners in the yard are a hazard to tires, feet and mowers, and it is reasonable to ask the crew to come back and sweep again.
What is cosmetic and what to raise before the warranty is filed
Cosmetic, in most cases: slight color differences between bundles, a small wobble in a course line that only shows in certain light, a little sealant at the ends of the ridge cap, scuffs on the gutters. Worth mentioning. Rarely worth holding anything up over.
Worth raising in writing: missing drip edge, caulk where step flashing should be, reused or missing boots, a ridge vent with no slot cut under it, soffit vents left blocked, exposed nails on the face of the roof, shingles that are already lifting, and nails left in the yard.
Raise these before the warranty registration is filed, and before final payment if you can. Ask the contractor who registers the manufacturer warranty, what it covers, and whether anything you noticed affects it. We do not know the terms of a warranty we have not read, and the manufacturer decides what it honors, not the crew.
None of this is a verdict you can reach on your own from the ground, and it is not meant to be. It is a list of things to look at and questions to ask. The answers you get back, and whether they are specific, will tell you a lot.