Why waste your limited modeling time on scratchbuilding this, when resin companies can do better and save you a lot of work? Recently a company called "Custom Dioramics" did 1/48th European constructions, both urban and rural, and I can attest to the high quality of what they did, not mere demolished walls in some cases, but full roofs intact buildings facades at about 3/4 depth. They were even available at Squadron for a while... You could even combine several sets to potentially create full depth two street facades constructions...
It is true what I saw from them was nowhere near as tall as the photo provided (which I did not initially see), but if you have two intact facades as tall as this it will be a bit hard to even see the street from above...
Facades this tall are an absolutely huge piece of work....
The OP question was a bit confusing to me as to what he meant: Sorry for my English: Two rows of "flats" suggested to me rows of separated bungalows or one-story houses... Hem... European wartime streets are typically either solid continuous sidewalk-butting facades with few interruptions (urban-like, even in a very small village), or just isolated country houses very far from the street, sometimes clustered on a steep slope or hollow.
There are really no old-style WWII European streets with "rows" of separate habitations: That is simply not typical of how things were done there until much later in the 60s or 70s (but is very typical of North America)...
I have lived in a small French village of about 2000 people, and I can tell you that as soon as you get into this very small village it is continuous solid facades just like in a large city... Outside of the "core" you get widely-spaced houses that are sometimes "clustered" to present yet more continuous facades, or, usually if it is post WWII, it can be a bungalow, but usually well away from the street and town center, with a large front lawn and rear garden.
A useful point to note is the importance, in many old-style small French villages, of all sorts of waist (or head) height very rough and thick looking stone walls, usually for "hiding" a front lawn garden or field, which are often the main thing flanking a kilometer long street, the isolated house being well away from the street, unlike the solid continuous facades which are almost always butting directly on the sidewalk. Note the sidewalks do not have the "segmented" look they have in North America: They are smooth continuous medium gray asphalt, often with "harder" edge of cement or stone...
"Rows of flats" are perhaps better described as "four or six stories facades", because in reality there could be anything in them: The back end of a multi-story store, offices, banks; The term "flats" seems a bit too specific for what they are...
The habitable roof photo provided seems more typical to me of very upscale Paris, and would be very complicated to build from scratch, in addition to being usually a sixth or seventh floor... An absolutely massive project!
Also, be wary of O scale buildings as a substitute for true 1/48th scale: "O" scale for the British, and maybe for most of Europe, is really 1/43, as with the metal cars, and this is really what dominates what is available for rail scenery as far as I can see... It can do if you are careful, but the doors will look tall...
I hope this helps. Good luck with your project!
Gaston