The vertical striping could be due to the shape of the roof, with the underlying rafters pushing out those parts directly beneath them, so leaving a hollow away from that (the difference is likely to be very small, so wouldn't show as variations in the roof's appearance otherwise, except maybe under very low-angle lighting). I agree the rafters will be likely the defining point though.

Keeping the look fairly straightforward sounds like a good plan!

Having lived only in places with tile or slate roofs, I can confirm Shessar's photos are indeed entirely accurate for both those materials. Slide, wind effects and thin ice/snow melt basically works from the top down, and outer roof edges facing more nearly into the current wind, so those will all tend to clear of snow first. This can be enhanced around objects sticking out of the roof like chimneys and stove pipes, especially where those are in use. There may also be some smoke discoloration of the snow near chimneys that are in heavy, regular use as well (albeit that also tends to mean snow there will melt faster as well - introducing foreign particulates to the ice/snow helps it melt faster generally, like applying salt to road and path ice).

Roof patches do tend to be harder edged than you've illustrated so far, and with a tendency to remain in the hollows a little longer than the ridges on shaped tiles, as you've already noted. There are a lot of variables however, and commonly, once the snow's started to melt on such roofs, it will tend to clear fairly quickly thereafter, unless there's fresh snowfall heavy enough to fill-in the cleared gaps.

There are things to be said for both options (plus of course, you can't assume everyone will wish to map somewhere where the snow falls in late autumn/early winter, thickens and only starts to thaw around the start of spring - i.e. the randomness of what happens in British winters!), and both are obviously buildings. However, the one with less snow cover has a bit more character to it, which would definitely support the idea you mentioned in your most recent post Sue.

Yeah, I'd settle on one or the other, I think.

The cart tracks look a little more like car tracks to my eye currently, although magical carts requiring no animals to pull them would produce something similar. And if reduced in size considerably, they would work for sledge or ski tracks.

For animal-pulled vehicles though, there should be prints - or more simply for this style, perhaps, simply a muddied/shadow pock-marked region - between the outer tracks.

Sleigh tracks might have a central runner track as well as the two outer ones (actually at the centre-front of the sleigh, but that's not very relevant to the look of the tracks), just to complicate things still further!

Oh, and some suitable carts and sleighs would be nice to have as well. ⛷️