Rental house - prefabricated house or "conventional" brick construction

One more stupid question... a guest bathroom in a 3-4-room apartment?

From a certain size onwards, definitely. In my opinion, a separate bathroom belongs to 4 rooms.

Regarding suggestions: just look on Pinterest or in Google image search, there you will find corresponding floor plans.

Here with us, the new apartments always have a guest WC, even if they are only 70 sqm in size. I think the future tenants will simply expect that in a new apartment, just like a cellar. To what extent is the construction of a multi-family house actually profitable? Such a house costs around 500,000 euros excluding the land. Don’t you have to rent it out for ages to ever recoup the construction costs? Isn’t an existing property much more profitable?

Best regards
Sabine

When I look at the prices for not too old existing properties here and consider that the building plot is already there... I think that building (having it built) yourself is not the worst idea. Of course, it takes an eternity to recoup the construction costs, but the value of the house remains as well. At the current interest rate, there is not much else left to do...

Sites where I could look at reasonably pre-planned apartments of that size? Just to get one or two ideas about what makes sense?

Google (e.g. "two-family house floor plan"), Pinterest, but also real estate listings on Immoscout & Co, or prefabricated house brochures (look under the bungalow category because of the single-story design). Bathrooms hardly under 5 sqm, kitchens and children's rooms about 10 sqm, bedrooms from 14 sqm, living rooms alone from 25 sqm (with dining area even more). Except for the bathroom, hardly any room will be narrower than 2 meters. Even in children's rooms, you want to be able to place the bed lengthwise or crosswise; comfortable passage widths start at 90 cm, which is also roughly the edge length of a shower cabin. Even guest toilets or cleaning/pantry rooms come to about 2 sqm. Look at apartment listings online, they often have floor plans (almost always with condominiums), and then go to the viewing. That way you have both plan and real comparison.

Bungalows are useless, they have a HAR/utility room and no staircase. The sensible search is simply for "Grundriss Etagenwohnung"

Bungalows are useless, they have a utility room (HAR/Hauswirtschaftsraum) and no staircase.

How nice that you come directly from Schlauberg. There are more and more bungalow designs for childless people (but with a study), with about 90 sqm it’s almost the same, and the utility room often has roughly the size and location of the staircase. Of course, it’s not suitable for exact replication, but it’s enough for orientation.