In reply to Mattyk:
Indirect comment - if you have a stone slab roof, are you in a conservation area? If so, make sure you check the difference that makes to your permitted development rights (the means by which you avoid needing to apply for planning permission.)
I much prefer the look of panels mounted "in-roof" with regular slate or tile roofs - that is in a recessed void where they replace the roofing materials instead of mounted over them on rails; This also seems to have benefits in reducing weirdness of wind effects on the upper outer edges of the array that can put weird forces on individual small slates. But, you do not have a regular slate roof!
I can't even begin to visualise how a sunken integrated in-roof array would work with a northern stone slab roof, typically there's so much irregularity in the size of the large stone tiles that they'll never mate at the interface to the sunken region of an in-roof system. If you butcher the slabs to fit a rectangular depression for an in-roof array, it's going to look weird. Really weird. Where-as when I've seen rail mounted systems over a stone slab roof it looks fine.
I'd suggest speaking with a couple of installers who specialise in doing North East off-grid installations; they're far more likely to have a lot of experience with stone slab roof installs as it's the high altitude barn conversions where a grid hookup is more expensive than an off-grid battery/electric system, and these often have stone slab roofs; for example https://nzeco.co.uk
Post edited at 23:11