FranklyTile changes the maths
Removing and handling concrete tile is heavier and slower than stripping composition shingle, and disposal costs more. On tile homes, the first question is whether the tile is being replaced or lifted and re-laid, because that choice moves the price more than anything else on the page.
Decking discovery
Nobody knows the sheathing condition until the covering is off. A written per-sheet price protects you from negotiating while a crew waits on an open roof. Its absence is not a saving.
Flashing and penetrations
Skylights, solar mounts, HVAC curbs, and wall intersections are where these roofs leak. Reused flashing is the quiet reason one bid is lower, and often the reason a new roof leaks in its first winter.
Ventilation is often quietly omitted
Attic ventilation affects how long the new roof lasts. If a contractor recommends changes, it should be priced as a line item you can accept or decline, not folded invisibly into a total.