What a metal roof quote should actually say
Metal quotes are harder to compare than shingle quotes, because more of the work is invisible once it is finished. These are the lines that separate a complete one from a thin one.
What kind of panel, and how it is held
Standing seam with concealed clips and exposed-fastener ribbed panel are two different products with two different lifespans and two different failure modes. The quote should name which one, not simply say metal.
On standing seam, ask whether the clips are fixed or floating. A long panel that cannot move as it heats will find another way to relieve itself, usually at the fastener.
The pieces that are not panel
Closures at the ridge, named as a product rather than implied. Eave and rake trim. Valley lining. Pipe flashings rated for metal rather than the rubber boot that came off the shingle roof.
And counterflashing wherever a roof meets a wall — let into the masonry, or fastened to the face of it. Those are two different prices and two different lifespans.
Snow, and the underlayment
Where snow guards go, and how they attach. Clamped to the seam, or screwed through the panel? The second means new holes, and new holes belong in the plan.
What underlayment goes under the metal, and how far up from the eave. Metal is unforgiving of what happens beneath it, because you cannot see any of it once the panels are on.
And who fixes what, later
The manufacturer warrants the finish; the contractor warrants the work. On metal the second is worth more, because almost everything that goes wrong is installation rather than material.