To my knowledge, a preliminary building inquiry does not necessarily have to be prepared by a person authorized to draw plans. Anyone can do it - at least that is how it is here in Saxony. I cannot recommend passing the matter on to the buyers, unless they are already lined up. At the time, I solved it by "building" the plot fictitiously according to the neighboring development and generally recognized and nowadays common key figures. Naturally, I tried to implement a generous development. I then submitted this as a preliminary inquiry including all development commitments from the utility providers to the building authority. That was also a good decision, as we initially received a rejection due to incorrect assumptions from the nature conservation authority. After these were refuted and the plot was tidied up, it was sold within a week.