Simplest option would be to use the colour drawing tool, and then add an RGB Matrix Process Effect to the whole map, set to "Gray". This will make everything look B&W - so you could design the entire map using the colour set-up, and have it all appear as greyscale in the finished item.

In case you're unsure about adding the Effect, when you open up the Drawing Sheets and Effects dialogue box (click on the rectangle marked "S:" with the name of the current Sheet in at the top of your CC3+ drawing window), click on any Sheet, then click the "Whole Drawing" radio button above the Sheets list.

Then click "Add", select "RGB Matrix Process" from the list this will call-up, and then click to highlight the RGB Matrix Process Effect that's now been added to the Whole Drawing list.

Then click "Edit". Once you're in the RGB Matrix Process dialogue box, click "Predefined", then "Gray" from that list, and finally "OK", and then (assuming you have something already drawn on your map to check), click "Apply" to see what it does.

Good luck!

If all you want to do is place individual symbols from one of the City Cliffs Cartographer's Annual sets, select your first symbol choice, then right click to call up the Symbol Parameters dialogue box. Once there, uncheck the "Smart tracking" box and check the "Disable smart symbols" box. Then you can just pick and add whichever of the cliff symbols you want to your map without them connecting to one another as they ordinarily do.

As a frontier post, it might be possible there'd be better defences around the doorway externally than there are currently. Indeed, it's possible there'd be no ground-level access at all, with the main doorway on the level above that, accessed by a narrow stairway externally. Certainly, reworking the building as an inn might alter the access options, but some of the defensive structures would likely still remain. That'd be a lot of extra work here though, I realise!

There is a problem with the fireplace walls defensively now though, in that these are both thinner than anywhere else, and heavily advertised on the outside by projecting beyond the main line of the walls. In reality, the fireplace flues would likely have been built into the walls to disguise this (and probably be smaller than are currently shown), or be reinforced externally to have the same thickness as the main walls. Orcs and ogres might be reckless, but they're also not necessarily as stupid as systems like D&D have sometimes portrayed them 😉

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.