The brick looks really good as is. However the larger stones on the corners, top and bottom of the 1st floor and around the lower windows I would paint a (light?)stone or concrete colour(I'd go for polly scale aged concrete.)
The cimmney area needs to be less black. try to get the same amount of soot on the chimmney as where it meets the roof. while your'e on the roof, paint some induvidual and groups of tiles a slightly lighter or darker colour and apply a "wash" of ultra-thinned black paint on the roof to highlight the recesses. dont get it even. variation in darkness is good
I'm going to go on a tangent and contradict some people

, but my observation is that the wood bits will be treated. most likely with creosote(a coal distillate =>black) which will weather to a brown-black colour over time. I wouldn't put the dabs of grey on the wood, but maybe mix up the brown-black colour by eye and don't mix it completely, so you get subtle variations
I doubt that the stairs would be unpainted wood but who knows. it's your model, sso you decide. If you do decide to go for bare wood, paint it light grey with a bit of brown as I don't think they creosote the small timbers
it might be a good idea to look for real life pictures of what your'e trying to achieve. Tamya weathering powders might be a good investment too
Have fun,
Kariosls