At the moment the rafters are not installed in the plane, centimeters stray. Lumber for counter-battens and laths are treated (50x50 and 25x100) and need to start nailing them, but they have a different section, plus or minus 5 mm on both. The distance between the rafters is 60cm, trusses need to nail in 5 cm, under the self-locking rebate. At what stage to align, on the counter-batten or crates? String along the rafters from the ridge down? Then under each board of purlins also stretch threads parallel to the ridge? What to put under the shingles and purlins, where there are gaps in height, so that it was convenient and did not fail over time? Advised siding cut into pieces and put it under. Maybe a spacer of metal, like washers? That is, what to put, when you need to compensate for the failure of a couple of millimeters, and that when in a centimeter? And at what point is it better to do, under the bars of counter-battens or under the boards of purlins?
We usually level with plywood. We cut plywood pads of 4.6 and 8 mm, you can dial in 2 mm increments. If it's not possible to level the rafters themselves. We make a counter-batten, and then along the outermost rafters we stretch strings, make pads under each batten along the outermost rafters. Then pull the string across, beat the rest, beat the battens, pull the next, padding, battens, etc., it turns out pretty quickly.
If the rafters are in the plane, then calibrate the bars and plank crates on the machine. And so, we deduce laths in the plane of the screws 6 * 80-120 with a full thread (there are such, without a smooth body). Lattice remains threaded on the screw threads at the required distance from the bar. On a thread straighten the top and bottom battens, and then move the slope of the rule from the board rib and align everything else.