Comparison offer solid vs. wood

200 sqm including basement at 500k will be a bit tight. The rule of thumb is 2,500 € / sqm (nowadays rather more) + 40,000-50,000 € additional construction costs + furniture/kitchen + outdoor facilities. Given the income, especially if another child is coming, I would build somewhat smaller, around 140 - 150 sqm.

What did the banks say? Especially since part of the income comes from self-employment...

Regarding the tenderability – which points would still be essential for this? Both providers have already received our wishes in the form of the floor plan. In addition, KfW 55 was required.

Simply writing "please offer as KfW 55" on a floor plan inevitably leads to a result where you end up comparing apples (= solid house minus x) with pears (= timber house minus y). You really can't work with that. A (professionally created) planning also includes its own definition of the scope of work in order to have a common denominator.

Our semi-detached house neighbors have already decided on the solid construction provider.

So you already know these people, and there is communication between you. Those are already two important advantages.

I strongly assume that we can save quite a bit if we hook up there.

I strongly urge you, in case of doubt (meaning if two providers are considered about equal), to lean very favorably toward choosing the same contractor as your neighbor. However, discounts, goodies, or synergy effects will be minimal at best. You can share the porta-potties ;-)

Some items are missing from the solid construction offer that are already included in the timber construction offer.

Which ones these are, we cannot know. The base slab is often missing in prefabricated houses. That usually makes a prefabricated house somewhat more expensive, about 10%. With the current situation regarding wood, the difference could be larger. Energy efficiency aside – even if the prefabricated house builder can do that cheaper, I would not consider that decisive. At least I wouldn’t. I would say that often one already carries the decision internally, whether solid or timber frame. How does the other build? It is not wise to build separately.