youre not holding me responsible if you fall or cut off a limb. That being said, start at the top and work your way down. Take off the roofing materials and throw them off. pull the sheathing. Go down to the level below it with a step ladder and cut out the beams one at a time. Repeat to bottom floor. Use a sawzall or a chain saw. You will also probably need a heavy duty pry bar for the rim joists anchored to the walls. You should probably have another guy to support the weight of the joists while you’re cutting them. Good luck.
Edit: it was late when I responded and I was tired. You may need an impact wrench for the rim joist, maybe a screw gun, depending on how it is attached.