It is a flat roof, to which the residents have no access, and is four stories up
Ah, that does complicate things a tad. That's probably higher than most people will attempt with ladders.
So apart from the consent issue; access tower, MEWP or scaffold.
Time to get shitty with the freeholder / management co.
Your insurance company might help you out here - call them.
@Dammit started
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ChasnotRobert
Howard
@Dammit
It is a flat roof, to which the residents have no access, and is four stories up