I think the middle ground is something like https://wudl.co.uk/ where your house is essentially put together from smaller modular pieces. This allows pre-construction and the efficiencies in "mass production" while allowing semi-customisation.

Local companies doing construction in Serbia will happily provide you with a plan as well as a building cost ahead of time.

However, plots and legal requirements differ significantly that in urban environments, it's hard to make the most of the plot without going custom (requirement to be that far away from the neighbour and the street, whether you can have windows facing that side or not, what kind of foundation is required by the terrain, etc).

You're probably right. It makes more sense to sell those mass-produced floorplans to architects, who will make slight tweaks for local conditions and perhaps pay via subscription, rather than directly to consumers who will probably just copy the floorplan .jpg and take that to the builder anyway.

People who want a house built want to build their house. Cookie cutter is for subdivisions and apartments, which those folks are often trying to escape.

Prefab houses are a thing and they aren't exactly rare. People escaping apartments usually complain about neighbors or lack of a garden, not about the floor plan.

They are pretty rare, at least here in the US, and widely seen as undesirable or 2nd-3rd tier at best.

Where I live, they aren't that rare. People like the fact that they can be built fast.

Near as I can tell from Googling around, they make up 2-6% if the US housing stock.

This is one of the corporations that has been popular in my country for the last 10 years or so:

https://www.rdrymarov.cz/en/all-about-building

I do not know the percentage of the housing stock either, but housing stock here is very conservative. Many people still live in 100+ year old houses. New houses are being built, but the turnover rate is probably less than 1 per cent of all units a year right now, due to the vast bureaucracy.

But among the newly built houses, I see quite a lot of prefabricated houses out of wood. And the process of building them is rather quick. Once the lot is ready, a semi and a crane arrive and the house just grows in front of your eyes. Brick houses take a lot longer to build.

In Hungary we had house templates since the socialism.

(following sites are in Hungarian)

https://kulcsrakesz.hu/tipushazak/

https://hellohaz.hu/tipushazak/

https://www.leier.hu/tipushazak

These are prefab houses. They are built in factory and then pieced together on site. What the poster was asking for was free/cheap plans to build a house, without support.

Kind of like open source design of a house.

Only the Leier one is prefab, the others are from protherm (clay) brick. And yes the planes there aren't free.

However there also exists a state level catalog of free (open source) templates as well:

https://www.oeny.hu/oeny/nmtk/mintatervek

It seems it's only available for Hungarian citizens, as it needs Hungarian Electric Id to login. I'm not sure it qualifies for open source but it's free as in beer to Hungarian citizens with the right to adapt the plan to your demands.

I wouldn't be surprised if the architects making the plans had catalogues with existing designs. I would however be surprised if they gave weeks/months of work to get them into compliance with non trivial legal requirements away for free.