Sheet count is across the ridge (cover width). Sheet length is down the slope. Plan span is neither.
On NZ Roof Tools the ordered length is slope length including the eave overhang already in the run, then rounded up 50 mm. A ridge tuck or drip that is not in that run still needs a written extra. Rafter calculator uses the same slope.
The number
Sloping run = horizontal run ÷ cos(pitch). Horizontal run is half the eave-to-eave span plus eave overhang (gable/hip) or full plan width plus overhang (skillion).
Example: 4.8 m horizontal at 10° ≈ 4.87 m slope. If eaves are already in that 4.8 m, do not add them again. If they are not, add the drip. Then round to how the yard cuts (here 50 mm).
True longrun is usually one sheet ridge-to-eave. End laps appear when you hit a truck, site, or expansion cap — set a sheet length cap on the takeoff.
Per section, then drainage
A 14 m house and a 6 m garage do not share a length (multi-section). Hips change waste, not the common-rafter slope on a simple equal-pitch hip.
If the rounded length passes the CoP “check capacity after …” figure, you get a warning, not a pass: corrugate 15 m, Six Rib 20 m, Hi Five/T-Rib 40 m, generic tray 60 m. Next: drainage run checks and the NZMRM maximum-run calculator with a HIRDS rainfall. Product sheet and CoP still win.