Individual houses do not necessarily cost more everywhere now, at least as far as the customizable floor plan is concerned. And what is luxury? Is luxury installing burglar-resistant windows or making them slightly larger than the standard? Is luxury installing KfW40 or a controlled residential ventilation system? At least it can be read that you are using the construction service description standard. Whether external painting is included, we do not know, nor whether the ZB includes an outdoor faucet. A washbasin as well as outdoor lighting is certainly not included but is usually desired in one’s new home. In this respect, you need to check for yourselves what you want or need that is not included in your construction service description. If you cannot verify this, you need to get a professional to review the construction service description for you. However, _additional costs_ will always arise, whether it is the better silicone resin plaster on the outside or the number of sockets inside; there is so much around the house that is obviously _not_ listed in the construction service description, plus hidden costs, maybe earthworks, maybe the foundation slab or the container? (However, these are all obvious additional costs...) As already said: 250 for KfW 40 is too little; something will be missing somewhere. Added to that are paving, rainwater connection, a decent carport. 290,000 might work (with a garden you don’t have to spend 14 days at the sea), but that just doesn’t add up... You rather read 320/330 plus kitchen. Read, read, read! Reading and acquiring knowledge you have to do yourself.