The windows aren't actually out of scale- I drew this in Graphics at school; it's got long, churchesque windows

U should make the windows smaller and it'll look much much better!

Thanks for comments, fixed the green's saturation and shadow under the roof 

Lovely, i like it! But there are some points to clear (IMHO): 1. grass is too simple, it may be useful to use other colours instead of only green. 2. Shadows are strange - there is a shadow of the postbox but there is no shadow on the roof.

your brightest green is too saturated otherwise it is a nice pixel art