Costs for a house including a granny flat

Hello,

My wife (29) and I (27) are about to build. (Kreis Heilbronn)

Out of curiosity, I applied for a building plot at my old municipality and immediately received an approval.
It is about 700 sqm of land. (24x28m)
The building plot is completely flat with clean soil.

Our plan is to build together with my parents-in-law. It should be a main apartment of about 120-140 sqm and a granny flat or extension of about 70 sqm.

A basement is not planned. Whether prefabricated house or solid house does not really matter to us. It should not be anything fancy.
We will do all the exterior work ourselves since my brother-in-law is a landscaper. We would also do the flooring, wallpapering, and all painting work ourselves.
We would get windows and doors very cheaply through my uncle. He has his own company in this regard.

What costs should we still expect for the rest?

What funding opportunities are possible besides 2x KfW funding (2x 150,000€ for 2 residential units)?

If all goes well, we will have a few meetings with construction companies in 4 weeks. (We already had appointments, but my wife and I tested positive for Corona)

We would be very happy to receive some answers.

Regards, Alex

Whether prefabricated house or solid house is actually not so important to us.

Prefabricated or solid house is not really a decision in this respect, as there are also stone wall houses made of panels manufactured in the hall. I see both types of prefabricated houses rather ruled out if all the window stuff is to be contracted out independently. In the "Experiences with construction companies" section you will also find some companies discussed from your area. Even if built "stone on stone", for planning inspiration you will usually find more building proposals for one-and-a-half family houses from the prefab house folks, especially from the classic timber frame panel builders. This is usually called a "multi-generation house". Nice that you already have a plot of land. These are mostly located in new development areas from the municipality, so you can check the development plan to see what is possible there. What does the usage template say? - with 700 sqm you should definitely be able to do something good.

If all goes well, we will have a few talks with construction companies in 4 weeks. ( We would have had appointments already, but my wife and I tested positive for Corona)

This can all be done via videoconference. Plans and offers can be sent by email.

.., then you have plenty of time to read up. Have fun in the forum :)

And remember, you say it now without much fuss. During the planning process, more wishes will come up, whether from the woman or from you ([Elektrik->Smart Home], etc.), which cost money. Since building material costs are currently skyrocketing, I would estimate about €2,600 per sqm for you. We are at €2,650 with a lot of extras, but according to the "old" prices. However, this is just an estimate; you will know more after discussions and comparing the construction service descriptions of the individual construction companies.