In general, one should keep in mind that no reputable contractor currently can seriously offer fixed prices that are valid for longer than 4 or 8 weeks. Therefore, index price clauses will probably prevail. And just to mention, what has been gained if a contractor today wins his customers for next year with a bunch of fixed prices that, due to procurement prices at the end of this year, put the contractor into an economic loss. The contractor goes bankrupt and the started or planned construction can then not be continued or started (provision interest).
This may be bitter for the wishes of some, but one should face reality and also question the motivation for building once again.
And by the way ... the interest rate development can currently take adventurous values even by today’s standards. Around 2000 (just over 20 years ago), the mortgage interest rate was between 5.5 and 6% ... that’s almost double what most people today calculate with for interest AND repayment.