The roof on my mothers house needs to be painted, and I would appreciate any advice or experiences on preparing an older Colorsteel roof.

The roof is a 30-year-old long-run Coloursteel (though I'm not entirely sure if it's genuine Coloursteel). The colour has come off about 3% of the roof, and in some areas, you can scratch the colour off with a fingernail.

After talking with Resene’s technical support, their recommendation was to waterblast the roof to remove as much of the remaining coating as possible.

Here are my questions:

Any recommendations for waterblasting services in the Nelson area?
Estimated cost for a single-story, two-bedroom home on flat land
General tips on prepping old Colorsteel for painting

Thanks