1. Floor plan without land is only conditionally useful. [B‘Plan, Baufenster, Hanglage etc] 2. As a tip, always draw furniture to scale 3. For Karlsruhe, rooftop terrace etc, take your budget times 2.
Start and create a room program. This includes important points for you like running meters of closet space, oversized bed, etc. Building is almost always a compromise between wishes and budget.