The drawing

Four things get recorded, and all four end up on the quote.

Slope: Marked in inches of rise per twelve. Under 3:12 is not a shingle roof, whatever anybody tells you.
Deck: Probed at every valley and eave. Soft sheathing is priced by the sheet on the quote, not discovered later.
Drainage: Where the water goes, including onto the neighbour's gable and into your own foundation.
Penetrations: Every pipe, vent, and chimney counted, because each one is a flashing detail and flashings are where roofs leak.

Why draw it at all?: Because a photograph flattens a roof and a roof is not flat. Two slopes meeting is a valley, and a valley is a detail, and details are where water gets in. A drawing makes those countable.
Why does the slope matter?: Under 3:12 a shingle roof is not a shingle roof, it is a membrane roof with shingles on it, and it will leak. Anybody quoting shingles on a 2:12 porch has either not measured or is hoping you will not.
Why probe the deck?: Soft sheathing is priced by the sheet on our quote, before the tear-off. Companies that do not probe it find it on day two and hand you a change order while your house is open.
Why count penetrations?: Every pipe, vent, and chimney is a flashing. A roof with eleven penetrations is a different job from one with three, and the quote should say which yours is.