On the ridge, sometimes two layers, sometimes one. Sometimes buckled.
Uneven, shingles "broken to length" instead of cut. Sometimes long, sometimes short.
Top of dormer where it meets the house. exposed nail, buckled shingles.
Crooked shingle line following crookedly installed drip edge. I don't think they ever snapped a line. All of the porch was done by the time I got home from work.
Transition between porch roof and main roof. Wanders all over the place.
Side "wraparound" porch roof. "Ski-slope" last course due to incorrect installation of drip edge.