The two words "metal roof" cover two products that are not close to each other in price, in installation, or in how they eventually fail. One hides every fastener under a raised seam. The other drives screws straight through the face of the panel and relies on a rubber washer under each screw head to keep the water out. Knowing which one you are being sold is the single most useful thing on this site.
Exposed fastener panel, and where you have already seen it
Corrugated and ribbed exposed fastener panel is the metal on farm buildings, pole barns, equipment sheds, lean-to carports and a great many back garden structures in St. Louis County. It is a perfectly reasonable product for those buildings. It is cheap, it goes down fast, it needs no seaming machine, and a competent person can install it with a drill.
The problem is not the panel. The problem is the fastener. Each screw passes through the metal and into the purlin or the deck, and sealing that hole is the job of a small rubber washer, usually EPDM, compressed under the screw head. That washer is on the outside of the roof. It is in direct sun, it goes through every freeze and thaw cycle a Missouri winter has, and it expands and contracts against a screw shank that is expanding and contracting at a different rate.
Rubber in that situation hardens. It cracks, it takes a permanent set, and it stops sealing. Meanwhile the panel is moving with temperature against the fixed screw, which slowly wallows the hole out. On a roof with several thousand screws in it, "a few of them have failed" is not an unusual condition, it is the expected condition at some point in the roof's life. Which is why maintenance on an exposed fastener roof genuinely means walking it and re-torquing or replacing fasteners, and why the warranty conversation on those roofs is so different.
You can do this from the pavement
Raised ribs, blank field
The ribs stand clearly above the flat of the panel, tall enough to cast their own shadow line. Between the ribs the metal is completely blank. No screw heads, no dots, no rows of anything.
The rib spacing is regular and the ribs run the full slope without interruption. Trim at the ridge, the rake and the eave is folded metal, usually fabricated for that roof.
Low ribs, rows of dots
The profile is shallower, often wavy rather than square, and there are visible regular rows of fastener heads marching across the panel, usually lining up with the framing underneath.
Look for horizontal laps as well. Exposed fastener sheets are frequently lapped part way up the slope, which standing seam panels are normally cut long enough to avoid.
Exposed fastener is not a scam, it is a different job
Plenty of St. Louis homeowners are perfectly well served by exposed fastener panel on a detached garage, a workshop, a carport or a pole building where the interior is not finished and a slow drip is an annoyance rather than a disaster. It is a fraction of the cost, it can be installed over purlins without a solid deck, and if a washer goes in ten years the fix is a screw.
What is not fair is selling it as though it were the other product, and the language makes that easy: both are "metal roofs", both are "steel", both come with a colour chart. The gap only shows up on the roof and in the price. If the panel is going over living space, on a plane you can see from the street, and you are paying a premium because you were told metal lasts longer than shingles, you should be certain which of the two you are buying.
Low slope sections, long runs, and the geometry test that decides whether your roof is a candidate at all.