I've managed to clear a few of those situations in various forms, using a 5m 2x1 baton with a piece of stiff ish wire on the end, formed in a long loop so it will slide down the pipe. I've cleared a few blockages this way.
The reason he is probably quibbling is because those blocks haven't been filled in between the joists which would add plenty of support at the edge of the roof. Why have the grp trims been fitted before the insulation?
I'm going with lower triangles sheathed out in half-inch ply, 5x2 timber sistered to the ridge, going as far down as practical, and some sort of timber ridge beam.
If you go to a decent builders merchants, you should be able to buy 10mm limestone in 25 kg bags, also grit sand in the same size, plus a bag of cement. you can then make your own, which will be much better for your job. Don't forget the feb mix.