Have a 4/12 roof with torch on on it rite now its a vaulted ceiling so they have insul board under torchon,they want to change to shingles,would ya put a cold roof over it or build up to same height as insul board and then sheath over it?

Here’s part of it.

tear it down to deck/ceiling, peel and stick or somekind of synthetic underlay on entire roof deck(vapour barrier on warm side of insulation that is coming)screw down 2x2 on top of 2x2 over rafters( only way I can think of to get a 2x4 like purlon system secure) 2" styrofoam insul between purlons, sheet with 1/2" , now underlay and shingle with ridgevent. Now the entire roof breaths and you have taken care of any moisture buildup with said vapour barrier. Aluminum louvred vents at bottom or smart vent(google it) on second course…
I have a job very similar to this in the hopper and the customer did not want to pay for this so they waived all warranty to just rip it and shingle it. I think they will have moisture issues in the future.
Hope this helps.