The local building authority has so far given the verbal approval for construction (there is no development plan as it is currently farmland). We only have to participate proportionally in the development costs, but that is okay for us.
If you not only read along here for a while but also browse back, you will find numerous comparable examples here that "close only counts in horseshoes." It's almost a running gag that someone thinks it's easy to turn their property into building land because you can spit over to a building area from there. From the previous descriptions, I cannot clearly see what constellation between "outer area" and planned or unplanned "inner area" we are dealing with here. If there is a §34 area adjacent, you will have to accept the insertion requirement; if an area with a development plan is adjacent, the expansion of its spatial scope will go faster (not quickly!!!), and presumably its framework requirements will be adopted (possibly the plan might also be changed on this occasion). So unfortunately, I see a high probability that first, your project will be at least a five-year plan, and second, the unusual roof shape will fall by the wayside.
Architects are popular in the forum, the costs are often set very high, and if someone says the floor plan is too complicated, another says they love the angles. If you want to plan "for later," someone writes, "then better build the next house later."
Architects are viewed mostly positively here, but especially people with opinions
specifically about the architects' estimating skills tend to be more skeptical. Here, about houses for "later," it is not just anyone writing but usually in favor from the perspective of the building consultant—mostly me—and with the background of having built a second time myself (but not retirement-near) and - I don't count here because she would likely have stayed loyal to the previous house without relocating several hundred kilometers. By and large, I would say the faction strengths of preparers and object changers are roughly balanced here (and the motives mostly individual—the almost general recommendation to change therefore comes almost only from me).
As I have already written, we will definitely work with an architect, but we also have to tell them what we want, and for that, I find a DIY preliminary planning with all the ideas we have important.
Good gracious, preferably not that!—even professional planning does not fully immunize against infections by images. So better steer the planner’s creativity onto no slippery ice at all. For yourselves, your own sketches—especially when conflicts become apparent—may help you clarify things, but better not show them to the expert (because of the poison magic of images). You will be happier with a joint draft, primarily developed by the expert, than with the approach of trying to "optimize" a self-made plan. The greatest danger is not even for the laypeople with their botched attempts, but explicitly for the drafts that are (allegedly or even "objectively") only in need of refinement.