Here I am not sure if I understand this correctly. When is the best time to decide on a general contractor (GU)?
That depends on how the question is to be understood, i.e. whether the emphasis is on "for ... GU" or on "deciding ... on one".
Overall, I do not assume that we want a very individual house. The only thing would be the number of floors, but that is not set in stone either.
As far as it means deciding on the path of a catalog design against the background of the mature serial model, it should hopefully be clear that this does not work with a model from the Meier catalog being built by Müller (and vice versa), because the Müller team has never built Meier models. So for this path, the house design and the team must come from the same stable. In this case, one requests with their preliminary design two offers: namely one for this house design and a second for the most similar serial model from the catalog of the respective provider. If Schulze is the winner, Schulze as GU is already determined and the architect's task is to develop the adjustments (i.e. to work similar to service phase 3). For this, it is not so bad to commission Schulze’s “house architect” in the double sense. However, this approach requires the courage to commit so early. Because a preliminary design is hardly suitable for developing a construction service description, so you have a lot of comparing offers to do. For this, service phase 4 follows here and derived working plans analogous to service phase 5 with the GU, who is already selected here.
This approach is suitable for prospective builders with the attitude of consumer goods buyers on a shopping tour for "1 piece house with xy square meters", who do not differ in this respect from their counterparts following the other design selection method (serial model vs. individual planning).
The approach of prospective builders I advise is different: they do not derive the selection of the GU from the answers in the preliminary inquiry round, but only the indication of the more favorable construction method in their specific case. It is a wisely invested small amount of money to entrust the execution and interpretation of the preliminary inquiry round to an independent consultant. The question of why to take a professional at all is quickly answered when you despair over the evaluation of the results. Once the decision "wood or stone" has been made, the client’s own architect – as already explained in more detail before, preferably the same as in module A – also handles modules B and C. The tender (service phase 7) is then addressed to bidders suitable according to the architect’s experience. Whether they then submit offers as GU or at least shell construction GU, I recommend not to restrict in advance.
Anyone who decides on a house in panel construction (regardless of whether wood frame, solid wood, concrete sandwich, expanded clay or whatever) will have their architect already coordinate with the manufacturer/system provider in service phase 3. A classic tender will therefore practically only occur with stone-on-stone houses, because otherwise the contractor is already fixed by the wall build-up (Krause does not manufacture walls according to Becker’s system and vice versa). Is the approach now understood?