Slipped slates, cracked tiles, failed flashing, storm damage and the damp patch on the ceiling that nobody can account for. Most roof repairs are small once you know where the water is actually getting in, and finding that is the part worth paying for. Callum goes up, has a look, and tells you what has failed and what it costs to put right.

Water runs along battens and rafters before it shows on a ceiling, so the stain is rarely under the hole. The roof gets looked at properly before anything is lifted.
Replacements matched to what is already up there, so a repair on a front elevation does not announce itself from the pavement.
Ridge tiles lifted by wind, slates off in a gale and flashing peeled back. Made safe first, repaired properly after.
You get told what has failed and what it costs before anything starts. No invoice that arrives bigger than the conversation.
Not always, and it is worth being honest about that up front. A ceiling stain can be a slipped slate, but it can equally be failed flashing round a chimney, a blocked gutter overflowing back under the tiles, condensation in a poorly ventilated loft, or a waste pipe in the floor above. The job on the first visit is to work out which of those it is, because the wrong diagnosis means paying for a repair that changes nothing. Callum will tell you if it is not a roofing problem.
Quickly, and usually the same week for anything actively letting water in. If it is running through a ceiling, ring rather than message and it gets prioritised. The first visit is about stopping the water and making it safe, which can be a temporary cover if the weather will not allow a proper repair that day, and the permanent fix follows once the roof is dry enough to work on properly.
Quotes are free. What that means in practice is that Callum will come out, get up and look at the roof, and tell you what is wrong and what it costs, without a bill for the visit. Where it changes is on a genuine emergency call-out where work is done there and then to stop damage, because that is a repair rather than a quote.
It depends why it slipped. If a single nail has corroded and the slate itself is sound it can be refixed with a clip and it will sit for years. If the slate is delaminating, or if half the nails on that elevation have gone the same way, putting one back is a job you will be repeating every winter. Callum will tell you which of the two you have got, and if a roof is genuinely at the end of its life he will say so rather than sell you a repair a year at a time.
Yes. Flat roof repairs are a regular job, usually on garages, dormers, porches and rear extensions where the covering has split, blistered or come away at an upstand. Same principle as a pitched roof: find where the water is genuinely getting in first, because a flat roof will happily leak two metres from the damage.
Not usually. Most single slate and tile repairs are done off ladders and a roof ladder safely and without the cost of a scaffold. Where the work is a whole elevation, a chimney, or anything at a height or pitch that cannot be reached safely, scaffolding goes up and it is priced into the quote so it is not a surprise later. Nobody is going to freehand a job that needs a proper platform.