I have acquired some windows from houses in HO scale that I have been using, and it kinda works, but I want to try and make my own. For this, I'll need a two part cast, and 10 mm windows are small! THe size I'm going for for a full size window is about 6x9 mm. That means the woodwork is made in 0,5 mm evergreen strips.
It took me the better part of an evening to finish one window, partially finish another (in another style) and finish one window frame, all of those without gap filling and sanding. On the plus side I have finally found a good use for my 5x magnifier glass.