ArchiCAD, AutoCAD, Nemetschek, VectorWorks, 2D or 3D. From €5,000 to €7,000 as a basic version. And then practice persistently for 1-2 years while designing and thoroughly planning 2-3 houses. That will lead to fairly good results. Provided one knows, wants, and can then implement it constructively. Expertise in building construction, building physics, structural engineering, and material science is certainly not a hindrance. Advanced knowledge of building and planning law is also quite beneficial. I naturally assume taste, style, and good spatial imagination are present. A certain level of originality, of course, as well. The cost accounting steps go without saying; I mention them only for the sake of formality. Now, the rest is really simple. It is hard to imagine, but some people spend/waste years on a so-called "degree" to learn exactly this. Curious, isn’t it!