Down payment for a new house? What do you think?

You will quickly realize: a payment plan in two installments, about 4% before the starting signal and then 96% after completion, that cannot honestly work, no developer has that much capital or will ever want to tie it up for so long through pre-financing.

Honestly, this is done relatively frequently in the developer business. The developer has to finance with the bank anyway. I currently have a developer project in Duisburg on my desk – purchase price payment only upon completion. He does pay somewhat more interest overall (cannot compensate like under the Broker and Developer Ordinance) but saves significantly on the processing fee, broker and developer ordinance guarantees, etc. The bank appreciates it, since the processing effort decreases drastically.

Honestly, this is done relatively often in the property development business. The developer has to finance with the bank one way or another. I currently have a development project in Duisburg on my desk – purchase price payment only upon completion.

I believe you mostly deal with "old school" developers who also bring the necessary capital resources and creditworthiness. However, in my perception, today – at least concerning the market segment of semi-detached houses – the type "wannabe / butcher shop developer" is the norm, who "finances" their business through payment plans, building from hand to mouth on demand, and taking plenty of high risks. Congratulations if you’re still dealing with professionals today – but I think you almost have to call that an island of the blessed, or it’s only still the norm in multi-family housing construction, while in the undergrowth the dilettantes and gamblers are at play. The description by the OP sounds to me like a real estate agent diversifying into development in cooperation with an architect-(mailbox) general contractor – both with correspondingly small-scale credit lines.