Rental house - prefabricated house or "conventional" brick construction

Yes, and it’s great to live here! What use is it if the room exists but does not fit the location of the staircase at all? That doesn’t get you anywhere. Therefore, you can simply use the logical search terms. And that has nothing to do with being a smart aleck, but simply with reaching the goal sensibly with the appropriate terms.

First question: What is easy to rent out in the area? Is there a university? Is it rural or urban? Rule: The smaller, the higher the price per square meter.
Who do I want to rent to? A three-room apartment works both for a young family with one child and for older people. A 45 sqm apartment is more likely only for singles. Four rooms, that’s already the size for fairly large families. It’s best to clarify these questions during a consultation hour with [Haus und Grund]. That’s basically the landlords' club. You’ll join as a landlord anyway, mainly because of the legal advice they offer.
The trick to get at least 5% return before taxes is to build appealing but cheaply (a new flat doesn’t need a guest toilet, people). This has to be clarified exactly with the contractor. That’s why the apartments all look roughly the same. That’s just how it’s done. Otherwise, it doesn’t add up. My 5 cent.

(No apartment on a floor needs a guest WC, guys).

But of course, because as you yourself say:

First question: What is easily rentable in the area?

In my district town (just big enough for a "lord" mayor), it roughly applies: 70 sqm clearly without, 90 sqm maybe, 120 sqm never without. You have to see relatively for yourself what is typical for the area. And you can also see that quickly again in the real estate listings.

So friends of ours live in Hamburg Rahlstedt renting, good location, about 65 sqm, two rooms, kitchen, one bathroom, hallway, basement room, well-maintained house, 12 thousand cold rent per year. In Hamburg, ownership is only possible for a few happy few. This kind of apartment pays off. I might get 4 units in such a house, without making it bigger than twice four rooms, then I have 48 thousand per year or a bit less, depending on where it is located. If you assume house plus land with 650, the return is right.

I’ll ask the question of all questions:

Why no semi-detached house? Is that not allowed according to [BePlan]?
A semi-detached house is much easier to rent out :)

And the question about the guest WC depends on whether you want the apartments to be of basic standard or move into the comfort zone. This is decided by the location and target group.

Regarding storage rooms: It is regulated somewhere how it must be handled in a rental building with parking spaces, storage for two-wheelers or baby carriages, drying rooms, etc. But it may also be that this does not apply to small rental properties.

Regards, Yvonne

Why not a duplex? Isn't that prohibited according to the development plan? One half of a duplex is much easier to rent out :)

I already touched on that in #4 and only noted that the tenant clientele is not the same. This should not be a counterargument, just a note; so far, I have not read any rejection from the original poster on this.