Aha, so we are talking about a real construction project, and the "outsourcing" of the child's room and study is mainly motivated by not wanting to accommodate the space requirements on fewer floors. A teenager will probably appreciate living "a bit further away from the action." Where does the planner’s price estimate come from in a DIY planning? The plot shows (in the area of the building footprint) about a one-meter rise away from the street. According to the 11ant basement rule, this means an optional basement. Basically, an amateur plan leads to about twenty percent more floor area and costs just due to lack of experience (excluding some generous square meters), so consulting an independent architect even pays off (as I generally advise to separate craft fun and real property ownership). Failed details have already been pointed out—I don’t need to say more in this regard, but I will later distribute my likes accordingly (meaning roughly: "I would have said something similar and just save all parties the double content").