Those round windows tops are a b*%%&r to do properly. I've tried various options over the years including scribing plasticard and bending individual strips of the stuff. Sometimes a commercial version will fit but then you have to buy loads of packs to get the size you want. The most successful technique seems to be choosing a prototype with rectangular windows so you don't have to bother.
Yesterday I mentioned my chad supply. Today I've used them to produce the characteristic splayed brickwork.
The method is simple - put a blob of Bostick all purpose on the workbench. Pick the chad up on the point of a knife. Dip chad in glue. Place on model. Do this 13 times and then shuffle the little card rectangles around until they look regular. Repeat for each window.
OK, it's not prefect - I should have cut every other chad in half to overlap the courses. They should be tighter packed too but I can live with all this for the sake of not going mad. In the context of a layout these sort of little niggles don't stand out as long as the overall impression is right. A philosophy even shared by the god-like (well if you remember his articles in old RM's) Alan Downes. And if he says it's right, who am I to argue ?