You can cut with carbide saw blade on a circular saw. Get the cheapest but you will have only about 10 cuts before blade is worn away. Set the blade so not to cut the sheathing but that's not exact practice. Lots of smaller cuts later. About 6x6 squares. Anything larger, you may not be able to handle. If body is concern, smaller cuts. Roof that big, you definitely want big heavy duty tarps enough to cover the whole roof and if flat, some way to seal them together. And ways to hold the tarp down and prepare for big winds. Don't hope for light breezes. Set up one area below for debris and best if you can rent a dumpster, position it close and dump into it.
Roof that big, I don't think this is diy, esp concerning weather. You can roof in stages, I guess, remove old in sections and roof that area, then move on. This increases the chance of damaging/traffic wear on new and will take lots more time. I was young so did it for my parents, actually similar size low slope roof. Gravel and about 1" hot tar/paper roof. Including later fiber board and standard roll roof that failed in just about 10 years. Point is I was young.
BTW, if you have just one layer of old roof, and roof frame is sturdy enough for more weight, you can roof over the old. Stripping the old roof has the benefit of finding frame damage, but often enough, you don't need to fix the frame to pristine conditions. Clean slate is what everybody likes but not always necessary/advised when compared to cost and risk of opening the roof.
