It is often thought that money can be saved by having a commercial building casco (wind- and watertight) built and buying the other work separately. What entrepreneurs usually do not realize is that they then have to coordinate everything themselves. And in the unlikely event that something goes wrong, you will have to provide the solution yourself. If this is not your daily work, it costs a lot of time that cannot be spent on your own operational management.
It is often small details that have a large (financial) impact. When parties work independently of each other, they bear responsibility for only one part. There is then a greater chance of miscommunication. Think of parts that just don’t fit properly, that are missing, that need to be adapted later or that fall between ship and shore. This often unnecessarily costs time, money and irritation.