This is a window I designed for my tabletop buildings. I scale them to 50% for 28mm heroic.

The size in the filename (4mm/5mm/6mm) is the width of the wall (assuming you also scale to 50%). I like the window frame to stick out a bit on the inside of the building so I use a size bigger than my wall thickness. If you use much thicker walls let me know and I'll make another version. If the difference is small, you should be fine just by scaling.

I print mine with the outside of the window facing up and use auto-generated supports from Cura.

I post my complete builds here:
https://www.instagram.com/xbogxhalo/