is this an issue

[billybob150811]

i have a quote from a roofer to strip the old mineral felt, and plywood underneath it and fix new 18mm osb and fit 3 ply new felt
today .a wet morning they turned up i am at work they put the osb over the old felt and ply could this cause an issue down the line or is this an industry norm in wet conditions
it creates a difference in height between myself and my neighbour as our flat roofs above respective bedrooms join

 

[DAZB]

If the quote was, as you said, to "strip the old mineral felt, and plywood underneath it and fix new 18mm osb and fit 3 ply new felt" then that is what they should have done and not avoided half the work by leaving on the existing layers. Ask them to do what you employed them to do or do the same to the neighbours to get them level again in lieu of not giving you what they are charging you for.