I will sometimes use poles to jack barn rafters.
get up there and nail a 2x to the bottom of the rafters. Clear the floor and nail a 2x parallel to the rafter run, a foot or three in from the upper jacking spot. Measure from top to bottom on a tilt, cut your pole so that you can drive the bottom of the pole along the floor of the barn(the lower 2x). Nail the top of your pole to the upper 2x first, or it will fall on you.
This is a bit hard to explain, but will lift the roof easily right off the top plate, using multiple poles spaced 4-8ft apart, depending on the weight of the roof system.