Hi:
Most shutters are between 12 and 18-inches wide. Doors, in this country are 3’x 6’8” on most residential buildings. Old structures like this may have wider doors, usually up to 3’-6”, but the height doesn’t increase much unless the story height is increased. These look like they have a short floor to floor height. Older buildings often have narrower windows, 24-30 inches wide. Remember, the stones will be of a size that a local mason could pick it up and lay it without a “crane”. Looks like a greenhouse on the back and the glass in it is probably about 4’-0” wide. Much more span and it gets pretty thick if you use it on the roof. Diamond shingles are usually in the range of 16-18-inches square.
Draw it up, build a rough model out of cardboard and see if the proportions look right. Adjust using a copy machine to enlarge or shrink the “plans” it till it looks right.
Neat little building. Just put my easy chair in the left corner of the greenhouse.
Ted