Well, that was your dad's job and his specialism. I studied Architecture for my first degree, and that did not include an extra 3 years studying engineering, or a 3 year apprenticeship in plumbing or how to wire electrics. These are specialisms in their own right and take time to learn. That's why big projects require teams of specialists. You can of course design buildings that do not require these extra professionals, but such buildings tend to be more basic and off the peg.