The buildings I've had for 6mm battles were rather... experimental (I have too much fondness of them to say they were primitive or ugly). As the campaign area broadens, the architecture must also change, and a great deal was learnt about miniature house construction from the previous attempts.
What we have here was constructed in a day, including painting and basing. Eleven buildings altogether, with a few more in progress not shown. All of them are made of paper, the L-shaped big house has a match stick support for its roof.
I start building these by laying out the walls on the paper, then calculate the dimensions of the roof. The only required tools are a set-square ruler, a pencil and a pair of sharp scissors.
I mark the surfaces with a ball-point pen before cutting them out. One of the mistakes I made with the previous line was using smaller pieces of card for doors and windows, glued on the surface of the walls. This way the windows were actually further out from the plane of the wall: in reality it is the other way around! So this time I simply marked the windows too, and did the same thing with the roof, so I could get an OK look without dotting on individual tiles.
I usually leave small excess strips of paper where the walls will be joined, and a pair on the bottom of the longer walls to be glued on the bases. No such thing for roofs. After a period of waiting (even superglue takes time to fully cure, and believe me, it murders paintbrushes) I prime the whole thing white, then use a darker color, followed by a drybrush, and then I pick out the details on the walls. The roof sometimes receives a dark (brown or black) wash before drybrushing.
Three stone houses with the French countryside in mind, but generic enough to be placed in most of imaginary Europe.
A Roman style stone church, again with the specific intention to be able to place it at any location from Italy to Northern Europe. I had some trouble with the towers but less with the semicircular wall section, it was pretty easy to calculate its length. I usually find that while I have absolutely no use of high school maths, these grade school mysteries can be engaging and easily solved. The things a master builder has to face!
Five small timber frame houses, German / Western European style.
Two larger timber frame buildings, more likely to be around town centers.
As the Calvacasa Rebellion proceeds, the chance of a 6mm battle also increases, so the following few buildings, after completing the surroundings of a German town square, will be Mediterranean, and then some smaller village buildings, followed by Middle Eastern flat-top houses. For what reason, you shall see soon.