Most textured paint seems quite coarse. The new stuff from Tamiya is the finest I can think of and I think it comes in white for snow and stipples but again is not the right texture for whitewashed plaster.
I have had some success with applying a coat of PVA, though varnish or paint should work almost as well, and pouring or literally throwing fine, dry play pit sand over it. This is the nicest, finest sand I have seen and comes in handy sized bags from the Early Learning Centre. This is coarser than stippling texture gel but much quicker and easier. I saw something the other day, a cooling tower I had tried to make from a waste paper bin, and on any other forum would that not sound mad, and it had the PVA and sand texture but made interesting by some flat strips where I had used masking tape to protect some areas.
This seems blindingly obvious but might we worth stating. I had intended to leave the brick bits untextured.
Lately I have been making mostly Dark Age to early medieval buildings for Saga, hence a lot of experience with towelling roofs, but before that were generic middle eastern ones which got the stippling or sand which was easier than plaster and dark age round houses which got either towelling or teddy bear fur roofs, the former being easier and better looking. I might use towelling for the Rouke's Drift buildings.
Would the shed and toilet roofs have been bare wood or tar paper? For the latter the model railway crowd recommend tissue paper, not the sort we use a lot of in winter but that for model aircraft or something called silk span. If anyone remembers the old civil service toilet paper, like very thin tracing paper, it might have worked. I bought some black crepe paper before Christmas to try on some wild west buildings but have dome nothing with it yet.

