Our Onduline roof is overdue for replacement and leaking, but what's the easiest way to remove the old roof? Some of it has screws but most of it uses the capped Onduline nails. They seem to be very resistant to pulling out with a claw hammer. Left to my own devices I'd bolt-crop the top off them, remove the sheet, and then remove what's left of the nails one by one with some mole grips, but I feel there must be a better way...!
They are ring-shank nails, so they are hard to pull by design.
You need a crow-bar, pry-bar, ripping bar, wrecking bar. Solid steel with the "claw" on a looped end, 2 or 3 feet long. Not a hammer. Apologize to your hammer if you haven't already wrecked it.
Preferable to leave the heads on, as it will be faster to rip them out with the bar if you don't have to put mole grips on each time, and take them off, and not impale yourself on a bunch of cut-off nails in the meantime. You can probably rip the glorified tar-paper roof off around them if you'd rather have it gone when you are removing the nails.
I have (the remains of) an Onduline roof I put on 20 years ago. I will be replacing it with metal - that was an experiment that has results I won't be repeating. The metal roofs I put on at the same time are in excellent shape.
I use a nail jack or crescent nail puller. I have demoed many decks and membrane roofs with this tool. It has a beak you place over the head, on nails that are set into the wood it takes a couple hits to get under the head but with washers I can usually grab the head and rock them right out. I have even used My nail jack to pull finishing nails out of hardie cement board trim.
The one thing I can say is to make sure you hold it properly or when you thump it you could get a blood blister. When the nails are tough like ring shanks are after I grab the head I lift the slide and pull and the are much easier even 16p galvanized come out I have never found a better method and I have every type of “paw” or “hoof” type puller and crow bars and wonder bars of every size and the nail jack is faster and creates less damage.