Dont have our own web address yet as were just starting up. But if you try bluelines roofing www.bluelinesroofing.co.uk thats who were working for, just mention us if you ring for a quote. Chris and Stuart Scott
Hi
If you went up there with a power hose you could actually end up causing damage. Your best bet would be to go up there with just a brush and try and brush the moss off, as for painting the tiles honestly it looks crap
If you say only half the roof is completed, he is probably waiting to finish the other side before filling the gables with mortar at the end, might be wrong but its the way some roofers use. I've used the dry verge before and can recommend it so maybe suggest to him using it? As its usually...